diff --git a/build.sbt b/build.sbt
index d54cf52f34..5b90c4c412 100644
--- a/build.sbt
+++ b/build.sbt
@@ -130,7 +130,6 @@ lazy val core = myCrossProject("core")
       Dependencies.catsParse,
       Dependencies.circeConfig,
       Dependencies.circeGeneric,
-      Dependencies.circeGenericExtras,
       Dependencies.circeParser,
       Dependencies.circeRefined,
       Dependencies.commonsIo,
diff --git a/docs/repo-specific-configuration.md b/docs/repo-specific-configuration.md
index 7fa70064f3..b28cc5c7df 100644
--- a/docs/repo-specific-configuration.md
+++ b/docs/repo-specific-configuration.md
@@ -130,7 +130,7 @@ updates.allowPreReleases  = [ { groupId = "com.example", artifactId="foo" } ]
 updates.limit = 5
 
 # The extensions of files that should be updated.
-# Default: [".mill-version",".sbt",".sbt.shared",".sc",".scala",".scalafmt.conf",".sdkmanrc",".yml","build.properties","mill-version","pom.xml"]
+# Default: [".mill",".mill-version",".sbt",".sbt.shared",".sc",".scala",".scalafmt.conf",".sdkmanrc",".yml","build.properties","mill-version","pom.xml"]
 updates.fileExtensions = [".scala", ".sbt", ".sbt.shared", ".sc", ".yml", ".md", ".markdown", ".txt"]
 
 # If "on-conflicts", Scala Steward will update the PR it created to resolve conflicts as
diff --git a/modules/benchmark/src/main/scala/org/scalasteward/benchmark/UpdatesConfigBenchmark.scala b/modules/benchmark/src/main/scala/org/scalasteward/benchmark/UpdatesConfigBenchmark.scala
index bfec02fb25..382c6c8f88 100644
--- a/modules/benchmark/src/main/scala/org/scalasteward/benchmark/UpdatesConfigBenchmark.scala
+++ b/modules/benchmark/src/main/scala/org/scalasteward/benchmark/UpdatesConfigBenchmark.scala
@@ -36,9 +36,9 @@ class UpdatesConfigBenchmark {
     val update = Update.ForArtifactId(dependency, newerVersions)
 
     UpdatesConfig().keep(update)
-    UpdatesConfig(allow = List(UpdatePattern(groupId, None, None))).keep(update)
+    UpdatesConfig(allow = Some(List(UpdatePattern(groupId, None, None)))).keep(update)
     UpdatesConfig(allow =
-      List(UpdatePattern(groupId, None, Some(VersionPattern(prefix = Some("6.0")))))
+      Some(List(UpdatePattern(groupId, None, Some(VersionPattern(prefix = Some("6.0"))))))
     ).keep(update)
   }
 }
diff --git a/modules/core/src/main/scala/org/scalasteward/core/application/Cli.scala b/modules/core/src/main/scala/org/scalasteward/core/application/Cli.scala
index c7eb1d5501..c174b029fc 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/application/Cli.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/application/Cli.scala
@@ -320,7 +320,7 @@ object Cli {
   private val defaultMavenRepo: Opts[Resolver] = {
     val default = Resolver.mavenCentral
     option[String]("default-maven-repo", s"default: ${default.location}")
-      .map(location => Resolver.MavenRepository("default", location, None, Nil))
+      .map(location => Resolver.MavenRepository("default", location, None, None))
       .withDefault(default)
   }
 
diff --git a/modules/core/src/main/scala/org/scalasteward/core/buildtool/maven/parser.scala b/modules/core/src/main/scala/org/scalasteward/core/buildtool/maven/parser.scala
index 2925ad64f2..d95ce1cc89 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/buildtool/maven/parser.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/buildtool/maven/parser.scala
@@ -72,7 +72,7 @@ object parser {
       id <- stringNoSpace
       _ <- wsp.rep0 ~ Parser.string("url:") ~ wsp
       url <- stringNoSpace
-    } yield Resolver.MavenRepository(id, url, None, Nil)
+    } yield Resolver.MavenRepository(id, url, None, None)
 
   def parseResolvers(input: List[String]): List[Resolver] =
     input.mkString.split("""\[INFO]""").toList.flatMap { line =>
diff --git a/modules/core/src/main/scala/org/scalasteward/core/buildtool/mill/parser.scala b/modules/core/src/main/scala/org/scalasteward/core/buildtool/mill/parser.scala
index 0932884b9d..b06dbe9c84 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/buildtool/mill/parser.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/buildtool/mill/parser.scala
@@ -54,7 +54,7 @@ object parser {
     *
     * @param artifactName
     *   name of the artifact parsed from the build file
-    * @param millVerion
+    * @param millVersion
     *   the current Mill version being used
     * @return
     *   the newly put together ArtifactId
@@ -127,13 +127,13 @@ object MillModule {
           url <- c.downField("url").as[String]
           creds <- c.downField("auth").as[Option[Resolver.Credentials]]
           headers <- c.downField("headers").as[Option[List[Resolver.Header]]]
-        } yield Resolver.MavenRepository(url, url, creds, headers.getOrElse(Nil))
+        } yield Resolver.MavenRepository(url, url, creds, headers)
       case "ivy" =>
         for {
           url <- c.downField("pattern").as[String]
           creds <- c.downField("auth").as[Option[Resolver.Credentials]]
           headers <- c.downField("headers").as[Option[List[Resolver.Header]]]
-        } yield Resolver.IvyRepository(url, url, creds, headers.getOrElse(Nil))
+        } yield Resolver.IvyRepository(url, url, creds, headers)
       case typ => Left(DecodingFailure(s"Not a matching resolver type, $typ", c.history))
     }
   }
diff --git a/modules/core/src/main/scala/org/scalasteward/core/buildtool/sbt/data/SbtVersion.scala b/modules/core/src/main/scala/org/scalasteward/core/buildtool/sbt/data/SbtVersion.scala
index eccd65d292..5a94099952 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/buildtool/sbt/data/SbtVersion.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/buildtool/sbt/data/SbtVersion.scala
@@ -18,14 +18,16 @@ package org.scalasteward.core.buildtool.sbt.data
 
 import cats.Order
 import cats.syntax.all._
-import io.circe.Codec
-import io.circe.generic.extras.semiauto._
+import io.circe.{Decoder, Encoder}
 
 final case class SbtVersion(value: String)
 
 object SbtVersion {
-  implicit val sbtVersionCodec: Codec[SbtVersion] =
-    deriveUnwrappedCodec
+  implicit val sbtVersionDecoder: Decoder[SbtVersion] =
+    Decoder[String].map(SbtVersion.apply)
+
+  implicit val sbtVersionEncoder: Encoder[SbtVersion] =
+    Encoder[String].contramap(_.value)
 
   implicit val sbtVersionOrder: Order[SbtVersion] =
     Order[String].contramap(_.value)
diff --git a/modules/core/src/main/scala/org/scalasteward/core/buildtool/sbt/data/ScalaVersion.scala b/modules/core/src/main/scala/org/scalasteward/core/buildtool/sbt/data/ScalaVersion.scala
index 859dfc4e23..2cbdf3a09c 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/buildtool/sbt/data/ScalaVersion.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/buildtool/sbt/data/ScalaVersion.scala
@@ -18,14 +18,16 @@ package org.scalasteward.core.buildtool.sbt.data
 
 import cats.Order
 import cats.syntax.all._
-import io.circe.Codec
-import io.circe.generic.extras.semiauto._
+import io.circe.{Decoder, Encoder}
 
 final case class ScalaVersion(value: String)
 
 object ScalaVersion {
-  implicit val scalaVersionCodec: Codec[ScalaVersion] =
-    deriveUnwrappedCodec
+  implicit val scalaVersionDecoder: Decoder[ScalaVersion] =
+    Decoder[String].map(ScalaVersion.apply)
+
+  implicit val scalaVersionEncoder: Encoder[ScalaVersion] =
+    Encoder[String].contramap(_.value)
 
   implicit val scalaVersionOrder: Order[ScalaVersion] =
     Order[String].contramap(_.value)
diff --git a/modules/core/src/main/scala/org/scalasteward/core/coursier/CoursierAlg.scala b/modules/core/src/main/scala/org/scalasteward/core/coursier/CoursierAlg.scala
index 9f8913f508..d768e80d62 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/coursier/CoursierAlg.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/coursier/CoursierAlg.scala
@@ -123,10 +123,10 @@ object CoursierAlg {
   private def toCoursierRepository(resolver: Resolver): Either[String, coursier.Repository] =
     resolver match {
       case Resolver.MavenRepository(_, location, creds, headers) =>
-        val authentication = toCoursierAuthentication(creds, headers)
+        val authentication = toCoursierAuthentication(creds, headers.getOrElse(Nil))
         Right(coursier.maven.SbtMavenRepository.apply(location, authentication))
       case Resolver.IvyRepository(_, pattern, creds, headers) =>
-        val authentication = toCoursierAuthentication(creds, headers)
+        val authentication = toCoursierAuthentication(creds, headers.getOrElse(Nil))
         coursier.ivy.IvyRepository.parse(pattern, authentication = authentication)
     }
 
diff --git a/modules/core/src/main/scala/org/scalasteward/core/data/CrossDependency.scala b/modules/core/src/main/scala/org/scalasteward/core/data/CrossDependency.scala
index ef78361b88..8d90238b37 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/data/CrossDependency.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/data/CrossDependency.scala
@@ -18,8 +18,7 @@ package org.scalasteward.core.data
 
 import cats.Order
 import cats.syntax.all._
-import io.circe.Codec
-import io.circe.generic.extras.semiauto._
+import io.circe.{Decoder, Encoder}
 import org.scalasteward.core.util.Nel
 
 /** A list of dependencies with the same groupId, (non-cross) artifactId, and version. */
@@ -44,9 +43,12 @@ object CrossDependency {
       .map(grouped => CrossDependency(grouped.sorted))
       .toList
 
-  implicit val crossDependencyCodec: Codec[CrossDependency] =
-    deriveUnwrappedCodec
+  implicit val crossDependencyDecoder: Decoder[CrossDependency] =
+    Decoder[Nel[Dependency]].map(CrossDependency.apply)
+
+  implicit val crossDependencyEncoder: Encoder[CrossDependency] =
+    Encoder[Nel[Dependency]].contramap(_.dependencies)
 
   implicit val crossDependencyOrder: Order[CrossDependency] =
-    Order.by((_: CrossDependency).dependencies)
+    Order.by(_.dependencies)
 }
diff --git a/modules/core/src/main/scala/org/scalasteward/core/data/Resolver.scala b/modules/core/src/main/scala/org/scalasteward/core/data/Resolver.scala
index 0944815b32..ec1ecd8ca4 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/data/Resolver.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/data/Resolver.scala
@@ -18,8 +18,6 @@ package org.scalasteward.core.data
 
 import cats.Order
 import io.circe.Codec
-import io.circe.generic.extras.Configuration
-import io.circe.generic.extras.semiauto.deriveConfiguredCodec
 import io.circe.generic.semiauto._
 import org.scalasteward.core.data.Resolver._
 
@@ -41,28 +39,27 @@ object Resolver {
   }
   final case class Header(key: String, value: String)
   object Header {
-    implicit val headerCodec: Codec[Header] = deriveCodec
+    implicit val headerCodec: Codec[Header] =
+      deriveCodec
   }
   final case class MavenRepository(
       name: String,
       location: String,
       credentials: Option[Credentials],
-      headers: List[Header] = Nil
+      headers: Option[List[Header]]
   ) extends Resolver
   final case class IvyRepository(
       name: String,
       pattern: String,
       credentials: Option[Credentials],
-      headers: List[Header] = Nil
+      headers: Option[List[Header]]
   ) extends Resolver
 
   val mavenCentral: MavenRepository =
-    MavenRepository("public", "https://repo1.maven.org/maven2/", None, Nil)
+    MavenRepository("public", "https://repo1.maven.org/maven2/", None, None)
 
-  implicit val resolverCodec: Codec[Resolver] = {
-    implicit val customConfig: Configuration = Configuration.default.withDefaults
-    deriveConfiguredCodec
-  }
+  implicit val resolverCodec: Codec[Resolver] =
+    deriveCodec
 
   implicit val resolverOrder: Order[Resolver] =
     Order.by {
diff --git a/modules/core/src/main/scala/org/scalasteward/core/data/Version.scala b/modules/core/src/main/scala/org/scalasteward/core/data/Version.scala
index 22c005d6a0..40edf369d7 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/data/Version.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/data/Version.scala
@@ -19,8 +19,7 @@ package org.scalasteward.core.data
 import cats.Order
 import cats.implicits._
 import cats.parse.{Numbers, Parser, Rfc5234}
-import io.circe.Codec
-import io.circe.generic.extras.semiauto.deriveUnwrappedCodec
+import io.circe.{Decoder, Encoder}
 import org.scalasteward.core.data.Version.startsWithDate
 
 final case class Version(value: String) {
@@ -128,8 +127,11 @@ object Version {
 
   val tagNames: List[Version => String] = List("v" + _, _.value, "release-" + _)
 
-  implicit val versionCodec: Codec[Version] =
-    deriveUnwrappedCodec
+  implicit val versionDecoder: Decoder[Version] =
+    Decoder[String].map(Version.apply)
+
+  implicit val versionEncoder: Encoder[Version] =
+    Encoder[String].contramap(_.value)
 
   implicit val versionOrder: Order[Version] =
     Order.from[Version] { (v1, v2) =>
diff --git a/modules/core/src/main/scala/org/scalasteward/core/edit/EditAlg.scala b/modules/core/src/main/scala/org/scalasteward/core/edit/EditAlg.scala
index 614b76d167..c95fc8335b 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/edit/EditAlg.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/edit/EditAlg.scala
@@ -113,14 +113,14 @@ final class EditAlg[F[_]](implicit
         fileAlg.editFile(repoDir / path, Substring.Replacement.applyAll[F](replacements))
       }
       _ <- reformatChangedFiles(data)
-      msgTemplate = data.config.commits.messageOrDefault
+      msgTemplate = data.config.commitsOrDefault.messageOrDefault
       commitMsg = CommitMsg.replaceVariables(msgTemplate)(update, data.repo.branch)
       maybeCommit <- gitAlg.commitAllIfDirty(data.repo, commitMsg, data.config.signoffCommits)
     } yield maybeCommit.map(UpdateEdit(update, _))
 
   private def reformatChangedFiles(data: RepoData): F[Unit] = {
-    val reformat =
-      data.config.scalafmt.runAfterUpgradingOrDefault && data.cache.dependsOn(List(scalafmtModule))
+    val reformat = data.config.scalafmtOrDefault.runAfterUpgradingOrDefault &&
+      data.cache.dependsOn(List(scalafmtModule))
     F.whenA(reformat) {
       data.config.buildRootsOrDefault(data.repo).traverse_ { buildRoot =>
         logger.attemptWarn.log_(s"Reformatting changed files failed in ${buildRoot.relativePath}") {
diff --git a/modules/core/src/main/scala/org/scalasteward/core/edit/hooks/HookExecutor.scala b/modules/core/src/main/scala/org/scalasteward/core/edit/hooks/HookExecutor.scala
index d3f3d85038..89ccba54ed 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/edit/hooks/HookExecutor.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/edit/hooks/HookExecutor.scala
@@ -173,7 +173,7 @@ object HookExecutor {
       useSandbox = false,
       commitMessage = update => CommitMsg(s"Reformat with scalafmt ${update.nextVersion}"),
       enabledByCache = _ => true,
-      enabledByConfig = _.scalafmt.runAfterUpgradingOrDefault,
+      enabledByConfig = _.scalafmtOrDefault.runAfterUpgradingOrDefault,
       addToGitBlameIgnoreRevs = true,
       signoffCommits = signoffCommits
     )
diff --git a/modules/core/src/main/scala/org/scalasteward/core/edit/scalafix/ScalafixMigrations.scala b/modules/core/src/main/scala/org/scalasteward/core/edit/scalafix/ScalafixMigrations.scala
index cb9fa4e10e..ce24e5c73e 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/edit/scalafix/ScalafixMigrations.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/edit/scalafix/ScalafixMigrations.scala
@@ -17,17 +17,11 @@
 package org.scalasteward.core.edit.scalafix
 
 import io.circe.Decoder
-import io.circe.generic.extras.Configuration
-import io.circe.generic.extras.semiauto._
+import io.circe.generic.semiauto._
 
-final case class ScalafixMigrations(
-    migrations: List[ScalafixMigration] = List.empty
-)
+final case class ScalafixMigrations(migrations: List[ScalafixMigration])
 
 object ScalafixMigrations {
-  implicit val configuration: Configuration =
-    Configuration.default.withDefaults
-
   implicit val scalafixMigrationsDecoder: Decoder[ScalafixMigrations] =
-    deriveConfiguredDecoder
+    deriveDecoder
 }
diff --git a/modules/core/src/main/scala/org/scalasteward/core/edit/update/ScannerAlg.scala b/modules/core/src/main/scala/org/scalasteward/core/edit/update/ScannerAlg.scala
index 8caef2659d..31615ed164 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/edit/update/ScannerAlg.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/edit/update/ScannerAlg.scala
@@ -66,7 +66,7 @@ final class ScannerAlg[F[_]](implicit
     Stream.eval(workspaceAlg.repoDir(repo)).flatMap { repoDir =>
       Stream
         .evalSeq(gitAlg.findFilesContaining(repo, string))
-        .filter(path => config.updates.fileExtensionsOrDefault.exists(path.endsWith))
+        .filter(path => config.updatesOrDefault.fileExtensionsOrDefault.exists(path.endsWith))
         .evalMapFilter(path => fileAlg.readFile(repoDir / path).map(_.map(FileData(path, _))))
     }
 }
diff --git a/modules/core/src/main/scala/org/scalasteward/core/forge/data/NewPullRequestData.scala b/modules/core/src/main/scala/org/scalasteward/core/forge/data/NewPullRequestData.scala
index 125c7fdc2e..d742b2806a 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/forge/data/NewPullRequestData.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/forge/data/NewPullRequestData.scala
@@ -270,7 +270,7 @@ object NewPullRequestData {
   ): NewPullRequestData =
     NewPullRequestData(
       title = CommitMsg
-        .replaceVariables(data.repoConfig.commits.messageOrDefault)(
+        .replaceVariables(data.repoConfig.commitsOrDefault.messageOrDefault)(
           data.update,
           data.repoData.repo.branch
         )
@@ -287,8 +287,8 @@ object NewPullRequestData {
       head = branchName,
       base = data.baseBranch,
       labels = if (addLabels) labels else List.empty,
-      assignees = data.repoConfig.assignees,
-      reviewers = data.repoConfig.reviewers
+      assignees = data.repoConfig.assigneesOrDefault,
+      reviewers = data.repoConfig.reviewersOrDefault
     )
 
   def updateTypeLabels(anUpdate: Update): List[String] = {
diff --git a/modules/core/src/main/scala/org/scalasteward/core/forge/data/PullRequestNumber.scala b/modules/core/src/main/scala/org/scalasteward/core/forge/data/PullRequestNumber.scala
index ede996ca4d..2fec40d112 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/forge/data/PullRequestNumber.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/forge/data/PullRequestNumber.scala
@@ -16,14 +16,16 @@
 
 package org.scalasteward.core.forge.data
 
-import io.circe.Codec
-import io.circe.generic.extras.semiauto.deriveUnwrappedCodec
+import io.circe.{Decoder, Encoder}
 
 final case class PullRequestNumber(value: Int) {
   override def toString: String = value.toString
 }
 
 object PullRequestNumber {
-  implicit val pullRequestNumberCodec: Codec[PullRequestNumber] =
-    deriveUnwrappedCodec
+  implicit val pullRequestNumberDecoder: Decoder[PullRequestNumber] =
+    Decoder[Int].map(PullRequestNumber.apply)
+
+  implicit val pullRequestNumberEncoder: Encoder[PullRequestNumber] =
+    Encoder[Int].contramap(_.value)
 }
diff --git a/modules/core/src/main/scala/org/scalasteward/core/nurture/NurtureAlg.scala b/modules/core/src/main/scala/org/scalasteward/core/nurture/NurtureAlg.scala
index ea07b921bc..b723055199 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/nurture/NurtureAlg.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/nurture/NurtureAlg.scala
@@ -51,7 +51,7 @@ final class NurtureAlg[F[_]](config: ForgeCfg)(implicit
       _ <- logger.info(s"Nurture ${data.repo.show}")
       baseBranch <- cloneAndSync(data.repo, fork)
       (grouped, notGrouped) = Update.groupByPullRequestGroup(
-        data.config.pullRequests.grouping,
+        data.config.pullRequestsOrDefault.groupingOrDefault,
         updates.toList
       )
       finalUpdates = Update.groupByGroupId(notGrouped) ++ grouped
@@ -80,7 +80,7 @@ final class NurtureAlg[F[_]](config: ForgeCfg)(implicit
           val updateData = UpdateData(data, fork, update, baseBranch, baseSha1, updateBranch)
           processUpdate(updateData)
         }
-        .through(util.takeUntilMaybe(0, data.config.updates.limit.map(_.value)) {
+        .through(util.takeUntilMaybe(0, data.config.updatesOrDefault.limit.map(_.value)) {
           case Ignored    => 0
           case Updated    => 1
           case Created(_) => 1
@@ -231,7 +231,8 @@ final class NurtureAlg[F[_]](config: ForgeCfg)(implicit
           .flatTraverse(gitAlg.findFilesContaining(data.repo, _))
           .map(_.distinct)
       allLabels = labelsFor(data.update, edits, filesWithOldVersion, artifactIdToVersionScheme)
-      labels = filterLabels(allLabels, data.repoData.config.pullRequests.includeMatchedLabels)
+      labels =
+        filterLabels(allLabels, data.repoData.config.pullRequestsOrDefault.includeMatchedLabels)
     } yield NewPullRequestData.from(
       data = data,
       branchName = config.tpe.pullRequestHeadFor(data.fork, data.updateBranch),
@@ -240,7 +241,7 @@ final class NurtureAlg[F[_]](config: ForgeCfg)(implicit
       artifactIdToUpdateInfoUrls = artifactIdToUpdateInfoUrls.toMap,
       filesWithOldVersion = filesWithOldVersion,
       addLabels = config.addLabels,
-      labels = data.repoData.config.pullRequests.customLabels ++ labels
+      labels = data.repoData.config.pullRequestsOrDefault.customLabelsOrDefault ++ labels
     )
 
   private def createPullRequest(data: UpdateData, edits: List[EditAttempt]): F[ProcessResult] =
@@ -309,7 +310,7 @@ final class NurtureAlg[F[_]](config: ForgeCfg)(implicit
 
   def closeRetractedPullRequests(data: RepoData): F[Unit] =
     pullRequestRepository
-      .getRetractedPullRequests(data.repo, data.config.updates.retracted)
+      .getRetractedPullRequests(data.repo, data.config.updatesOrDefault.retractedOrDefault)
       .flatMap {
         _.traverse_ { case (oldPr, retractedArtifact) =>
           closeRetractedPullRequest(data, oldPr, retractedArtifact)
diff --git a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/CommitsConfig.scala b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/CommitsConfig.scala
index c17e090d76..00885c52b2 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/CommitsConfig.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/CommitsConfig.scala
@@ -18,11 +18,10 @@ package org.scalasteward.core.repoconfig
 
 import cats.{Eq, Monoid}
 import io.circe.Codec
-import io.circe.generic.extras.Configuration
-import io.circe.generic.extras.semiauto._
+import io.circe.generic.semiauto.deriveCodec
 
 final case class CommitsConfig(
-    message: Option[String] = None
+    private val message: Option[String] = None
 ) {
   def messageOrDefault: String =
     message.getOrElse(CommitsConfig.defaultMessage)
@@ -34,11 +33,8 @@ object CommitsConfig {
   implicit val commitsConfigEq: Eq[CommitsConfig] =
     Eq.fromUniversalEquals
 
-  implicit val commitsConfigConfiguration: Configuration =
-    Configuration.default.withDefaults
-
   implicit val commitsConfigCodec: Codec[CommitsConfig] =
-    deriveConfiguredCodec
+    deriveCodec
 
   implicit val commitsConfigMonoid: Monoid[CommitsConfig] =
     Monoid.instance(CommitsConfig(), (x, y) => CommitsConfig(message = x.message.orElse(y.message)))
diff --git a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/GroupRepoConfig.scala b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/GroupRepoConfig.scala
index 97e7c69057..134725f803 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/GroupRepoConfig.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/GroupRepoConfig.scala
@@ -17,7 +17,6 @@
 package org.scalasteward.core.repoconfig
 
 import io.circe.Codec
-import io.circe.generic.extras.Configuration
 import io.circe.generic.semiauto.deriveCodec
 import org.scalasteward.core.data.Update
 import org.scalasteward.core.util.string.indentLines
@@ -28,9 +27,6 @@ final case class GroupRepoConfig(
 )
 
 object GroupRepoConfig {
-  implicit val groupPullConfigCodecConfig: Configuration =
-    Configuration.default.withDefaults
-
   implicit val groupPullConfigCodec: Codec[GroupRepoConfig] =
     deriveCodec
 
diff --git a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/PostUpdateHookConfig.scala b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/PostUpdateHookConfig.scala
index 077254220f..f5db495c60 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/PostUpdateHookConfig.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/PostUpdateHookConfig.scala
@@ -17,8 +17,7 @@
 package org.scalasteward.core.repoconfig
 
 import io.circe.Codec
-import io.circe.generic.extras.Configuration
-import io.circe.generic.extras.semiauto.deriveConfiguredCodec
+import io.circe.generic.semiauto.deriveCodec
 import org.scalasteward.core.data.{ArtifactId, GroupId}
 import org.scalasteward.core.edit.hooks.PostUpdateHook
 import org.scalasteward.core.git.CommitMsg
@@ -47,9 +46,6 @@ final case class PostUpdateHookConfig(
 }
 
 object PostUpdateHookConfig {
-  implicit val postUpdateHooksConfigConfiguration: Configuration =
-    Configuration.default.withDefaults
-
   implicit val postUpdateHooksConfigCodec: Codec[PostUpdateHookConfig] =
-    deriveConfiguredCodec
+    deriveCodec
 }
diff --git a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/PullRequestsConfig.scala b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/PullRequestsConfig.scala
index 39fef7b22c..a1f3f1ec32 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/PullRequestsConfig.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/PullRequestsConfig.scala
@@ -19,20 +19,24 @@ package org.scalasteward.core.repoconfig
 import cats.implicits._
 import cats.{Eq, Monoid}
 import io.circe.Codec
-import io.circe.generic.extras.Configuration
-import io.circe.generic.extras.semiauto.deriveConfiguredCodec
-
+import io.circe.generic.semiauto.deriveCodec
 import java.util.regex.PatternSyntaxException
 import scala.util.matching.Regex
 
 final case class PullRequestsConfig(
     frequency: Option[PullRequestFrequency] = None,
-    grouping: List[PullRequestGroup] = Nil,
+    private val grouping: Option[List[PullRequestGroup]] = None,
     includeMatchedLabels: Option[Regex] = None,
-    customLabels: List[String] = Nil
+    private val customLabels: Option[List[String]] = None
 ) {
   def frequencyOrDefault: PullRequestFrequency =
     frequency.getOrElse(PullRequestsConfig.defaultFrequency)
+
+  def groupingOrDefault: List[PullRequestGroup] =
+    grouping.getOrElse(Nil)
+
+  def customLabelsOrDefault: List[String] =
+    customLabels.getOrElse(Nil)
 }
 
 object PullRequestsConfig {
@@ -41,16 +45,13 @@ object PullRequestsConfig {
   implicit val pullRequestsConfigEq: Eq[PullRequestsConfig] =
     Eq.fromUniversalEquals
 
-  implicit val pullRequestsConfigConfiguration: Configuration =
-    Configuration.default.withDefaults
-
   implicit val regexCodec: Codec[Regex] =
     Codec
       .from[String](implicitly, implicitly)
       .iemap(s => Either.catchOnly[PatternSyntaxException](s.r).leftMap(_.getMessage))(_.regex)
 
   implicit val pullRequestsConfigCodec: Codec[PullRequestsConfig] =
-    deriveConfiguredCodec
+    deriveCodec
 
   implicit val pullRequestsConfigMonoid: Monoid[PullRequestsConfig] =
     Monoid.instance(
diff --git a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/RepoConfig.scala b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/RepoConfig.scala
index 46b20122a5..3e0b502630 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/RepoConfig.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/RepoConfig.scala
@@ -19,8 +19,7 @@ package org.scalasteward.core.repoconfig
 import cats.syntax.all._
 import cats.{Eq, Monoid}
 import io.circe.Codec
-import io.circe.generic.extras.Configuration
-import io.circe.generic.extras.semiauto._
+import io.circe.generic.semiauto._
 import io.circe.syntax._
 import org.scalasteward.core.buildtool.BuildRoot
 import org.scalasteward.core.data.Repo
@@ -28,24 +27,45 @@ import org.scalasteward.core.edit.hooks.PostUpdateHook
 import org.scalasteward.core.repoconfig.RepoConfig.defaultBuildRoots
 
 final case class RepoConfig(
-    commits: CommitsConfig = CommitsConfig(),
-    pullRequests: PullRequestsConfig = PullRequestsConfig(),
-    scalafmt: ScalafmtConfig = ScalafmtConfig(),
-    updates: UpdatesConfig = UpdatesConfig(),
-    postUpdateHooks: Option[List[PostUpdateHookConfig]] = None,
-    updatePullRequests: Option[PullRequestUpdateStrategy] = None,
-    buildRoots: Option[List[BuildRootConfig]] = None,
-    assignees: List[String] = List.empty,
-    reviewers: List[String] = List.empty,
-    dependencyOverrides: List[GroupRepoConfig] = List.empty,
+    private val commits: Option[CommitsConfig] = None,
+    private val pullRequests: Option[PullRequestsConfig] = None,
+    private val scalafmt: Option[ScalafmtConfig] = None,
+    private val updates: Option[UpdatesConfig] = None,
+    private val postUpdateHooks: Option[List[PostUpdateHookConfig]] = None,
+    private val updatePullRequests: Option[PullRequestUpdateStrategy] = None,
+    private val buildRoots: Option[List[BuildRootConfig]] = None,
+    private val assignees: Option[List[String]] = None,
+    private val reviewers: Option[List[String]] = None,
+    private val dependencyOverrides: Option[List[GroupRepoConfig]] = None,
     signoffCommits: Option[Boolean] = None
 ) {
+  def commitsOrDefault: CommitsConfig =
+    commits.getOrElse(CommitsConfig())
+
+  def pullRequestsOrDefault: PullRequestsConfig =
+    pullRequests.getOrElse(PullRequestsConfig())
+
+  def scalafmtOrDefault: ScalafmtConfig =
+    scalafmt.getOrElse(ScalafmtConfig())
+
+  def updatesOrDefault: UpdatesConfig =
+    updates.getOrElse(UpdatesConfig())
+
   def buildRootsOrDefault(repo: Repo): List[BuildRoot] =
     buildRoots
       .map(_.filterNot(_.relativePath.contains("..")))
       .getOrElse(defaultBuildRoots)
       .map(cfg => BuildRoot(repo, cfg.relativePath))
 
+  def assigneesOrDefault: List[String] =
+    assignees.getOrElse(Nil)
+
+  def reviewersOrDefault: List[String] =
+    reviewers.getOrElse(Nil)
+
+  def dependencyOverridesOrDefault: List[GroupRepoConfig] =
+    dependencyOverrides.getOrElse(Nil)
+
   def postUpdateHooksOrDefault: List[PostUpdateHook] =
     postUpdateHooks.getOrElse(Nil).map(_.toHook)
 
@@ -53,7 +73,7 @@ final case class RepoConfig(
     updatePullRequests.getOrElse(PullRequestUpdateStrategy.default)
 
   def show: String =
-    this.asJson.spaces2
+    this.asJson.deepDropNullValues.spaces2
 }
 
 object RepoConfig {
@@ -65,11 +85,8 @@ object RepoConfig {
   implicit val repoConfigEq: Eq[RepoConfig] =
     Eq.fromUniversalEquals
 
-  implicit val repoConfigConfiguration: Configuration =
-    Configuration.default.withDefaults
-
   implicit val repoConfigCodec: Codec[RepoConfig] =
-    deriveConfiguredCodec
+    deriveCodec
 
   implicit val repoConfigMonoid: Monoid[RepoConfig] =
     Monoid.instance(
diff --git a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/ScalafmtConfig.scala b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/ScalafmtConfig.scala
index e1f72dcec1..e5e05391c9 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/ScalafmtConfig.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/ScalafmtConfig.scala
@@ -18,11 +18,10 @@ package org.scalasteward.core.repoconfig
 
 import cats.{Eq, Monoid}
 import io.circe.Codec
-import io.circe.generic.extras.Configuration
-import io.circe.generic.extras.semiauto.deriveConfiguredCodec
+import io.circe.generic.semiauto.deriveCodec
 
 final case class ScalafmtConfig(
-    runAfterUpgrading: Option[Boolean] = None
+    private val runAfterUpgrading: Option[Boolean] = None
 ) {
   def runAfterUpgradingOrDefault: Boolean =
     runAfterUpgrading.getOrElse(ScalafmtConfig.defaultRunAfterUpgrading)
@@ -34,11 +33,8 @@ object ScalafmtConfig {
   implicit val scalafmtConfigEq: Eq[ScalafmtConfig] =
     Eq.fromUniversalEquals
 
-  implicit val scalafmtConfigConfiguration: Configuration =
-    Configuration.default.withDefaults
-
   implicit val scalafmtConfigCodec: Codec[ScalafmtConfig] =
-    deriveConfiguredCodec
+    deriveCodec
 
   implicit val scalafmtConfigMonoid: Monoid[ScalafmtConfig] =
     Monoid.instance(
diff --git a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/UpdatesConfig.scala b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/UpdatesConfig.scala
index a2521ce487..624ae2112e 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/repoconfig/UpdatesConfig.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/repoconfig/UpdatesConfig.scala
@@ -19,8 +19,7 @@ package org.scalasteward.core.repoconfig
 import cats.implicits._
 import cats.{Eq, Monoid}
 import eu.timepit.refined.types.numeric.NonNegInt
-import io.circe.generic.extras.Configuration
-import io.circe.generic.extras.semiauto._
+import io.circe.generic.semiauto.deriveCodec
 import io.circe.refined._
 import io.circe.{Codec, Decoder}
 import org.scalasteward.core.buildtool.maven.pomXmlName
@@ -38,14 +37,29 @@ import org.scalasteward.core.update.FilterAlg.{
 import org.scalasteward.core.util.{combineOptions, intellijThisImportIsUsed, Nel}
 
 final case class UpdatesConfig(
-    pin: List[UpdatePattern] = List.empty,
-    allow: List[UpdatePattern] = List.empty,
-    allowPreReleases: List[UpdatePattern] = List.empty,
-    ignore: List[UpdatePattern] = List.empty,
-    retracted: List[RetractedArtifact] = List.empty,
+    private val pin: Option[List[UpdatePattern]] = None,
+    private val allow: Option[List[UpdatePattern]] = None,
+    private val allowPreReleases: Option[List[UpdatePattern]] = None,
+    private val ignore: Option[List[UpdatePattern]] = None,
+    private val retracted: Option[List[RetractedArtifact]] = None,
     limit: Option[NonNegInt] = defaultLimit,
-    fileExtensions: Option[List[String]] = None
+    private val fileExtensions: Option[List[String]] = None
 ) {
+  private[repoconfig] def pinOrDefault: List[UpdatePattern] =
+    pin.getOrElse(Nil)
+
+  private def allowOrDefault: List[UpdatePattern] =
+    allow.getOrElse(Nil)
+
+  def allowPreReleasesOrDefault: List[UpdatePattern] =
+    allowPreReleases.getOrElse(Nil)
+
+  private def ignoreOrDefault: List[UpdatePattern] =
+    ignore.getOrElse(Nil)
+
+  def retractedOrDefault: List[RetractedArtifact] =
+    retracted.getOrElse(Nil)
+
   def fileExtensionsOrDefault: Set[String] =
     fileExtensions.fold(UpdatesConfig.defaultFileExtensions)(_.toSet)
 
@@ -56,14 +70,14 @@ final case class UpdatesConfig(
     isAllowedPreReleases(update)
 
   private def isAllowedPreReleases(update: Update.ForArtifactId): FilterResult = {
-    val m = UpdatePattern.findMatch(allowPreReleases, update, include = true)
+    val m = UpdatePattern.findMatch(allowPreReleasesOrDefault, update, include = true)
     if (m.filteredVersions.nonEmpty)
       Right(update)
     else Left(NotAllowedByConfig(update))
   }
 
   private def isAllowed(update: Update.ForArtifactId): FilterResult = {
-    val m = UpdatePattern.findMatch(allow, update, include = true)
+    val m = UpdatePattern.findMatch(allowOrDefault, update, include = true)
     if (m.filteredVersions.nonEmpty)
       Right(update.copy(newerVersions = Nel.fromListUnsafe(m.filteredVersions)))
     else if (allow.isEmpty)
@@ -72,7 +86,7 @@ final case class UpdatesConfig(
   }
 
   private def isPinned(update: Update.ForArtifactId): FilterResult = {
-    val m = UpdatePattern.findMatch(pin, update, include = true)
+    val m = UpdatePattern.findMatch(pinOrDefault, update, include = true)
     if (m.filteredVersions.nonEmpty)
       Right(update.copy(newerVersions = Nel.fromListUnsafe(m.filteredVersions)))
     else if (m.byArtifactId.isEmpty)
@@ -81,7 +95,7 @@ final case class UpdatesConfig(
   }
 
   private def isIgnored(update: Update.ForArtifactId): FilterResult = {
-    val m = UpdatePattern.findMatch(ignore, update, include = false)
+    val m = UpdatePattern.findMatch(ignoreOrDefault, update, include = false)
     if (m.filteredVersions.nonEmpty)
       Right(update.copy(newerVersions = Nel.fromListUnsafe(m.filteredVersions)))
     else
@@ -92,6 +106,7 @@ final case class UpdatesConfig(
 object UpdatesConfig {
   val defaultFileExtensions: Set[String] =
     Set(
+      ".mill",
       MillAlg.millVersionName,
       MillAlg.millVersionNameInConfig,
       ".sbt",
@@ -110,11 +125,8 @@ object UpdatesConfig {
   implicit val updatesConfigEq: Eq[UpdatesConfig] =
     Eq.fromUniversalEquals
 
-  implicit val updatesConfigConfiguration: Configuration =
-    Configuration.default.withDefaults
-
   implicit val updatesConfigCodec: Codec[UpdatesConfig] =
-    deriveConfiguredCodec
+    deriveCodec
 
   implicit val updatesConfigMonoid: Monoid[UpdatesConfig] =
     Monoid.instance(
@@ -125,7 +137,7 @@ object UpdatesConfig {
           allow = mergeAllow(x.allow, y.allow),
           allowPreReleases = mergeAllow(x.allowPreReleases, y.allowPreReleases),
           ignore = mergeIgnore(x.ignore, y.ignore),
-          retracted = x.retracted ::: y.retracted,
+          retracted = x.retracted |+| y.retracted,
           limit = x.limit.orElse(y.limit),
           fileExtensions = mergeFileExtensions(x.fileExtensions, y.fileExtensions)
         )
@@ -133,12 +145,13 @@ object UpdatesConfig {
 
   //  Strategy: union with repo preference in terms of revision
   private[repoconfig] def mergePin(
-      x: List[UpdatePattern],
-      y: List[UpdatePattern]
-  ): List[UpdatePattern] =
+      x: Option[List[UpdatePattern]],
+      y: Option[List[UpdatePattern]]
+  ): Option[List[UpdatePattern]] = combineOptions(x, y) { (x, y) =>
     x.filterNot { p1 =>
       y.exists(p2 => p1.groupId === p2.groupId && p1.artifactId === p2.artifactId)
     } ::: y
+  }
 
   private[repoconfig] val nonExistingUpdatePattern: List[UpdatePattern] =
     List(UpdatePattern(GroupId("non-exist"), None, None))
@@ -146,9 +159,9 @@ object UpdatesConfig {
   //  Strategy: superset
   //  Xa.Ya.Za |+| Xb.Yb.Zb
   private[repoconfig] def mergeAllow(
-      x: List[UpdatePattern],
-      y: List[UpdatePattern]
-  ): List[UpdatePattern] =
+      x: Option[List[UpdatePattern]],
+      y: Option[List[UpdatePattern]]
+  ): Option[List[UpdatePattern]] = combineOptions(x, y) { (x, y) =>
     (x, y) match {
       case (Nil, second) => second
       case (first, Nil)  => first
@@ -168,6 +181,7 @@ object UpdatesConfig {
         if (builder.isEmpty) nonExistingUpdatePattern
         else builder.distinct.toList
     }
+  }
 
   //  merge UpdatePattern for same group id
   private def mergeAllowGroupId(
@@ -207,10 +221,11 @@ object UpdatesConfig {
 
   //  Strategy: union
   private[repoconfig] def mergeIgnore(
-      x: List[UpdatePattern],
-      y: List[UpdatePattern]
-  ): List[UpdatePattern] =
+      x: Option[List[UpdatePattern]],
+      y: Option[List[UpdatePattern]]
+  ): Option[List[UpdatePattern]] = combineOptions(x, y) { (x, y) =>
     x ::: y.filterNot(x.contains)
+  }
 
   private[repoconfig] def mergeFileExtensions(
       x: Option[List[String]],
diff --git a/modules/core/src/main/scala/org/scalasteward/core/update/FilterAlg.scala b/modules/core/src/main/scala/org/scalasteward/core/update/FilterAlg.scala
index ca600df4e2..edfc4aa697 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/update/FilterAlg.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/update/FilterAlg.scala
@@ -66,7 +66,10 @@ object FilterAlg {
   final case class IgnoreScalaNext(update: Update.ForArtifactId) extends RejectionReason
 
   def localFilter(update: Update.ForArtifactId, repoConfig: RepoConfig): FilterResult =
-    repoConfig.updates.keep(update).flatMap(scalaLTSFilter).flatMap(globalFilter(_, repoConfig))
+    repoConfig.updatesOrDefault
+      .keep(update)
+      .flatMap(scalaLTSFilter)
+      .flatMap(globalFilter(_, repoConfig))
 
   def scalaLTSFilter(update: Update.ForArtifactId): FilterResult =
     if (!isScala3Lang(update))
@@ -107,7 +110,7 @@ object FilterAlg {
       repoConfig: RepoConfig
   ): FilterResult = {
     val newerVersions = update.newerVersions.toList
-    val maybeNext = repoConfig.updates.preRelease(update) match {
+    val maybeNext = repoConfig.updatesOrDefault.preRelease(update) match {
       case Left(_)  => update.currentVersion.selectNext(newerVersions)
       case Right(_) => update.currentVersion.selectNext(newerVersions, allowPreReleases = true)
     }
diff --git a/modules/core/src/main/scala/org/scalasteward/core/update/PruningAlg.scala b/modules/core/src/main/scala/org/scalasteward/core/update/PruningAlg.scala
index d8cbc9872c..d1fc340146 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/update/PruningAlg.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/update/PruningAlg.scala
@@ -166,7 +166,7 @@ final class PruningAlg[F[_]](implicit
       repoConfig: RepoConfig
   ): F[Boolean] = {
     val (frequencyz: Option[PullRequestFrequency], lastPrCreatedAt: Option[Timestamp]) =
-      repoConfig.dependencyOverrides
+      repoConfig.dependencyOverridesOrDefault
         .collectFirstSome { groupRepoConfig =>
           val matchResult = UpdatePattern
             .findMatch(List(groupRepoConfig.dependency), dependencyOutdated.update, include = true)
@@ -174,7 +174,7 @@ final class PruningAlg[F[_]](implicit
             (groupRepoConfig.pullRequests.frequency, artifactLastPrCreatedAt)
           )
         }
-        .getOrElse((repoConfig.pullRequests.frequency, repoLastPrCreatedAt))
+        .getOrElse((repoConfig.pullRequestsOrDefault.frequency, repoLastPrCreatedAt))
     val frequency = frequencyz.getOrElse(PullRequestFrequency.Asap)
 
     val dep = dependencyOutdated.crossDependency.head
diff --git a/modules/core/src/main/scala/org/scalasteward/core/update/artifact/ArtifactChange.scala b/modules/core/src/main/scala/org/scalasteward/core/update/artifact/ArtifactChange.scala
index 4b886e5ca9..54c502a294 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/update/artifact/ArtifactChange.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/update/artifact/ArtifactChange.scala
@@ -17,7 +17,7 @@
 package org.scalasteward.core.update.artifact
 
 import io.circe.Decoder
-import io.circe.generic.extras.{semiauto, Configuration}
+import io.circe.generic.semiauto
 import org.scalasteward.core.data.GroupId
 
 final case class ArtifactChange(
@@ -28,12 +28,9 @@ final case class ArtifactChange(
 )
 
 object ArtifactChange {
-  implicit val configuration: Configuration =
-    Configuration.default.withDefaults
-
-  implicit val decoder: Decoder[ArtifactChange] =
+  implicit val artifactChangeDecoder: Decoder[ArtifactChange] =
     semiauto
-      .deriveConfiguredDecoder[ArtifactChange]
+      .deriveDecoder[ArtifactChange]
       .ensure(
         change => change.groupIdBefore.isDefined || change.artifactIdBefore.isDefined,
         "At least one of groupIdBefore and/or artifactIdBefore must be set"
diff --git a/modules/core/src/main/scala/org/scalasteward/core/update/artifact/ArtifactChanges.scala b/modules/core/src/main/scala/org/scalasteward/core/update/artifact/ArtifactChanges.scala
index b258ba7c91..03680296e8 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/update/artifact/ArtifactChanges.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/update/artifact/ArtifactChanges.scala
@@ -17,14 +17,11 @@
 package org.scalasteward.core.update.artifact
 
 import io.circe.Decoder
-import io.circe.generic.extras.{semiauto, Configuration}
+import io.circe.generic.semiauto._
 
 final case class ArtifactChanges(changes: List[ArtifactChange])
 
 object ArtifactChanges {
-  implicit val configuration: Configuration =
-    Configuration.default.withDefaults
-
   implicit val artifactChangesDecoder: Decoder[ArtifactChanges] =
-    semiauto.deriveConfiguredDecoder
+    deriveDecoder
 }
diff --git a/modules/core/src/main/scala/org/scalasteward/core/util/Timestamp.scala b/modules/core/src/main/scala/org/scalasteward/core/util/Timestamp.scala
index 012e279486..38762de6c1 100644
--- a/modules/core/src/main/scala/org/scalasteward/core/util/Timestamp.scala
+++ b/modules/core/src/main/scala/org/scalasteward/core/util/Timestamp.scala
@@ -17,8 +17,7 @@
 package org.scalasteward.core.util
 
 import cats.Order
-import io.circe.Codec
-import io.circe.generic.extras.semiauto.deriveUnwrappedCodec
+import io.circe.{Decoder, Encoder}
 import java.time.{Instant, LocalDateTime, ZoneOffset}
 import java.util.concurrent.TimeUnit
 import scala.concurrent.duration.FiniteDuration
@@ -38,8 +37,11 @@ object Timestamp {
   def fromLocalDateTime(ldt: LocalDateTime): Timestamp =
     Timestamp(ldt.toInstant(ZoneOffset.UTC).toEpochMilli)
 
-  implicit val timestampCodec: Codec[Timestamp] =
-    deriveUnwrappedCodec
+  implicit val timestampDecoder: Decoder[Timestamp] =
+    Decoder[Long].map(Timestamp.apply)
+
+  implicit val timestampEncoder: Encoder[Timestamp] =
+    Encoder[Long].contramap(_.millis)
 
   implicit val timestampOrder: Order[Timestamp] =
     Order.by(_.millis)
diff --git a/modules/core/src/test/scala/org/scalasteward/core/TestInstances.scala b/modules/core/src/test/scala/org/scalasteward/core/TestInstances.scala
index ef87a73f46..e7f66e9a7a 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/TestInstances.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/TestInstances.scala
@@ -150,9 +150,9 @@ object TestInstances {
         limit <- Arbitrary.arbitrary[Option[NonNegInt]]
         fileExtensions <- Arbitrary.arbitrary[Option[List[String]]]
       } yield UpdatesConfig(
-        pin = pin,
-        allow = allow,
-        ignore = ignore,
+        pin = Some(pin),
+        allow = Some(allow),
+        ignore = Some(ignore),
         limit = limit,
         fileExtensions = fileExtensions
       )
@@ -161,10 +161,10 @@ object TestInstances {
   implicit val repoConfigArbitrary: Arbitrary[RepoConfig] =
     Arbitrary(
       for {
-        commits <- Arbitrary.arbitrary[CommitsConfig]
-        pullRequests <- Arbitrary.arbitrary[PullRequestsConfig]
-        scalafmt <- Arbitrary.arbitrary[ScalafmtConfig]
-        updates <- Arbitrary.arbitrary[UpdatesConfig]
+        commits <- Arbitrary.arbitrary[Option[CommitsConfig]]
+        pullRequests <- Arbitrary.arbitrary[Option[PullRequestsConfig]]
+        scalafmt <- Arbitrary.arbitrary[Option[ScalafmtConfig]]
+        updates <- Arbitrary.arbitrary[Option[UpdatesConfig]]
         updatePullRequests <- Arbitrary.arbitrary[Option[PullRequestUpdateStrategy]]
       } yield RepoConfig(
         commits = commits,
diff --git a/modules/core/src/test/scala/org/scalasteward/core/TestSyntax.scala b/modules/core/src/test/scala/org/scalasteward/core/TestSyntax.scala
index 125830752b..d8718acfa7 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/TestSyntax.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/TestSyntax.scala
@@ -7,7 +7,7 @@ import org.scalasteward.core.util.Nel
 object TestSyntax {
   val sbtPluginReleases: IvyRepository = {
     val pattern = "https://repo.scala-sbt.org/scalasbt/sbt-plugin-releases/[defaultPattern]"
-    IvyRepository("sbt-plugin-releases", pattern, None)
+    IvyRepository("sbt-plugin-releases", pattern, None, None)
   }
 
   implicit class GenericOps[A](val self: A) extends AnyVal {
diff --git a/modules/core/src/test/scala/org/scalasteward/core/buildtool/maven/parserTest.scala b/modules/core/src/test/scala/org/scalasteward/core/buildtool/maven/parserTest.scala
index 797579d8cc..a2ffcbaa51 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/buildtool/maven/parserTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/buildtool/maven/parserTest.scala
@@ -64,10 +64,10 @@ class parserTest extends FunSuite {
         "sonatype-nexus-snapshots",
         "https://oss.sonatype.org/content/repositories/snapshots",
         None,
-        Nil
+        None
       ),
-      MavenRepository("bintrayakkamaven", "https://dl.bintray.com/akka/maven/", None, Nil),
-      MavenRepository("apache.snapshots", "http://repository.apache.org/snapshots", None, Nil)
+      MavenRepository("bintrayakkamaven", "https://dl.bintray.com/akka/maven/", None, None),
+      MavenRepository("apache.snapshots", "http://repository.apache.org/snapshots", None, None)
     )
     assertEquals(resolvers, expected)
   }
diff --git a/modules/core/src/test/scala/org/scalasteward/core/buildtool/mill/MillDepParserTest.scala b/modules/core/src/test/scala/org/scalasteward/core/buildtool/mill/MillDepParserTest.scala
index 4afae0611d..cd7c4f334a 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/buildtool/mill/MillDepParserTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/buildtool/mill/MillDepParserTest.scala
@@ -2,6 +2,7 @@ package org.scalasteward.core.buildtool.mill
 
 import munit.FunSuite
 import org.scalasteward.core.TestSyntax._
+import org.scalasteward.core.data.Resolver
 
 class MillDepParserTest extends FunSuite {
   test("parse dependencies from https://github.com/lihaoyi/requests-scala") {
@@ -137,4 +138,13 @@ class MillDepParserTest extends FunSuite {
 
     assertEquals(result.find(_.name == "requests[2.13.0]").map(_.dependencies), Some(dep13))
   }
+
+  test("parse an IvyRepository") {
+    val pattern =
+      "https://repo.scala-sbt.org/scalasbt/sbt-plugin-releases/[organisation]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)([branch]/)[revision]/[type]s/[artifact](-[classifier]).[ext]"
+    val json = s""" { "pattern": "$pattern", "type": "ivy", "headers": [] } """
+    val obtained = io.circe.parser.decode(json)(MillModule.resolverDecoder)
+    val expected = Right(Resolver.IvyRepository(pattern, pattern, None, Some(Nil)))
+    assertEquals(obtained, expected)
+  }
 }
diff --git a/modules/core/src/test/scala/org/scalasteward/core/buildtool/sbt/parserTest.scala b/modules/core/src/test/scala/org/scalasteward/core/buildtool/sbt/parserTest.scala
index 8d19646ff1..f35b0b9e17 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/buildtool/sbt/parserTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/buildtool/sbt/parserTest.scala
@@ -28,7 +28,7 @@ class parserTest extends FunSuite {
          |[info] { "groupId": "com.dwijnand", "artifactId": { "name": "sbt-travisci", "maybeCrossName": null }, "version": "1.1.3",  "sbtVersion": "1.0" }
          |[info] { "groupId": "com.eed3si9n", "artifactId": { "name": "sbt-assembly", "maybeCrossName": null }, "version": "0.14.8", "sbtVersion": "1.0", "configurations": "foo" }
          |{ "groupId": "org.scalameta", "artifactId": { "name": "sbt-scalafmt", "maybeCrossName": null }, "version": "2.4.6", "sbtVersion": "1.0", "scalaVersion": "2.12", "configurations": null }
-         |[info] { "IvyRepository" : { "name": "sbt-plugin-releases", "pattern": "https://repo.scala-sbt.org/scalasbt/sbt-plugin-releases/[organisation]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)([branch]/)[revision]/[type]s/[artifact](-[classifier]).[ext]", "headers": [] } }
+         |[info] { "IvyRepository" : { "name": "sbt-plugin-releases", "pattern": "https://repo.scala-sbt.org/scalasbt/sbt-plugin-releases/[organisation]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)([branch]/)[revision]/[type]s/[artifact](-[classifier]).[ext]" } }
          |[info] { "IvyRepository" : { "name": "sbt-plugin-releases-with-creds", "pattern": "https://repo.scala-sbt.org/scalasbt/sbt-plugin-releases/[organisation]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)([branch]/)[revision]/[type]s/[artifact](-[classifier]).[ext]", "credentials": { "user": "tony", "pass": "m0ntana" }, "headers": [] } }
          |[info] --- snip ---
          |""".stripMargin.linesIterator.toList
@@ -45,19 +45,19 @@ class parserTest extends FunSuite {
             "bintray-ovotech-maven",
             "https://dl.bintray.com/ovotech/maven/",
             None,
-            Nil
+            Some(Nil)
           ),
           MavenRepository(
             "confluent-release",
             "http://packages.confluent.io/maven/",
             Some(Credentials("donny", "brasc0")),
-            Nil
+            Some(Nil)
           ),
           MavenRepository(
             "gitlab-internal",
             "http://gitlab.example.com/maven/",
             None,
-            List(Resolver.Header("private-token", "token123"))
+            Some(List(Resolver.Header("private-token", "token123")))
           )
         )
       ),
@@ -76,13 +76,13 @@ class parserTest extends FunSuite {
             "sbt-plugin-releases",
             "https://repo.scala-sbt.org/scalasbt/sbt-plugin-releases/[organisation]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)([branch]/)[revision]/[type]s/[artifact](-[classifier]).[ext]",
             None,
-            Nil
+            None
           ),
           IvyRepository(
             "sbt-plugin-releases-with-creds",
             "https://repo.scala-sbt.org/scalasbt/sbt-plugin-releases/[organisation]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)([branch]/)[revision]/[type]s/[artifact](-[classifier]).[ext]",
             Some(Credentials("tony", "m0ntana")),
-            Nil
+            Some(Nil)
           )
         )
       )
diff --git a/modules/core/src/test/scala/org/scalasteward/core/coursier/CoursierAlgTest.scala b/modules/core/src/test/scala/org/scalasteward/core/coursier/CoursierAlgTest.scala
index b6e516f069..ed981d97aa 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/coursier/CoursierAlgTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/coursier/CoursierAlgTest.scala
@@ -103,7 +103,7 @@ class CoursierAlgTest extends CatsEffectSuite {
   test("getMetadata: resolver with headers") {
     val dep = "org.typelevel".g % ("cats-effect", "cats-effect_2.12").a % "1.0.0"
     val resolvers =
-      List(Resolver.mavenCentral.copy(headers = List(Resolver.Header("X-Foo", "bar"))))
+      List(Resolver.mavenCentral.copy(headers = Some(List(Resolver.Header("X-Foo", "bar")))))
     val obtained =
       coursierAlg.getMetadata(dep, resolvers).runA(MockState.empty).map(_.repoUrl.isDefined)
     assertIOBoolean(obtained)
diff --git a/modules/core/src/test/scala/org/scalasteward/core/edit/hooks/HookExecutorTest.scala b/modules/core/src/test/scala/org/scalasteward/core/edit/hooks/HookExecutorTest.scala
index 7aa0de4acb..f6164df406 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/edit/hooks/HookExecutorTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/edit/hooks/HookExecutorTest.scala
@@ -93,7 +93,7 @@ class HookExecutorTest extends CatsEffectSuite {
 
   test("scalafmt: disabled by config") {
     val repoConfig =
-      RepoConfig.empty.copy(scalafmt = ScalafmtConfig(runAfterUpgrading = Some(false)))
+      RepoConfig.empty.copy(scalafmt = ScalafmtConfig(runAfterUpgrading = Some(false)).some)
     val data = RepoData(repo, dummyRepoCache, repoConfig)
     val update = (scalafmtGroupId % scalafmtArtifactId % "2.7.4" %> "2.7.5").single
     val state = hookExecutor.execPostUpdateHooks(data, update).runS(MockState.empty)
diff --git a/modules/core/src/test/scala/org/scalasteward/core/forge/data/NewPullRequestDataTest.scala b/modules/core/src/test/scala/org/scalasteward/core/forge/data/NewPullRequestDataTest.scala
index 3ae0a0f50f..8c05d78009 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/forge/data/NewPullRequestDataTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/forge/data/NewPullRequestDataTest.scala
@@ -11,8 +11,8 @@ import org.scalasteward.core.edit.scalafix.ScalafixMigration
 import org.scalasteward.core.forge.data.NewPullRequestData._
 import org.scalasteward.core.git.{Branch, Commit}
 import org.scalasteward.core.nurture.UpdateInfoUrl
-import org.scalasteward.core.util.Nel
 import org.scalasteward.core.repoconfig.RepoConfig
+import org.scalasteward.core.util.Nel
 
 class NewPullRequestDataTest extends FunSuite {
   test("bodyFor()") {
@@ -736,7 +736,7 @@ class NewPullRequestDataTest extends FunSuite {
       repoData = RepoData(
         repo = Repo("foo", "bar"),
         cache = dummyRepoCache,
-        config = RepoConfig(assignees = List("foo"), reviewers = List("bar"))
+        config = RepoConfig(assignees = Some(List("foo")), reviewers = Some(List("bar")))
       ),
       fork = Repo("scala-steward", "bar"),
       update = ("ch.qos.logback".g % "logback-classic".a % "1.2.0" %> "1.2.3").single,
@@ -844,7 +844,7 @@ class NewPullRequestDataTest extends FunSuite {
       repoData = RepoData(
         repo = Repo("foo", "bar"),
         cache = dummyRepoCache,
-        config = RepoConfig(assignees = List("foo"), reviewers = List("bar"))
+        config = RepoConfig(assignees = Some(List("foo")), reviewers = Some(List("bar")))
       ),
       fork = Repo("scala-steward", "bar"),
       update = update,
diff --git a/modules/core/src/test/scala/org/scalasteward/core/nurture/NurtureAlgTest.scala b/modules/core/src/test/scala/org/scalasteward/core/nurture/NurtureAlgTest.scala
index 1cdf3e6e6c..7fd62721d3 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/nurture/NurtureAlgTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/nurture/NurtureAlgTest.scala
@@ -22,8 +22,11 @@ class NurtureAlgTest extends CatsEffectSuite with Http4sDsl[MockEff] {
     val repoCache = dummyRepoCache.copy(dependencyInfos =
       List(List(DependencyInfo(dependency, Nil)).withMavenCentral)
     )
-    val repoData =
-      RepoData(repo, repoCache, RepoConfig(assignees = List("foo"), reviewers = List("bar")))
+    val repoData = RepoData(
+      repo,
+      repoCache,
+      RepoConfig(assignees = List("foo").some, reviewers = List("bar").some)
+    )
     val fork = Repo("scala-steward", "scala-steward")
     val update = (dependency %> "3.4.0").single
     val baseBranch = Branch("main")
@@ -134,8 +137,11 @@ class NurtureAlgTest extends CatsEffectSuite with Http4sDsl[MockEff] {
     val repoCache = dummyRepoCache.copy(dependencyInfos =
       List(List(DependencyInfo(dependency, Nil)).withMavenCentral)
     )
-    val repoData =
-      RepoData(repo, repoCache, RepoConfig(assignees = List("foo"), reviewers = List("bar")))
+    val repoData = RepoData(
+      repo,
+      repoCache,
+      RepoConfig(assignees = List("foo").some, reviewers = List("bar").some)
+    )
     val fork = Repo("scala-steward", "scala-steward")
     val update = (dependency %> "3.4.0").single
     val baseBranch = Branch("main")
@@ -171,11 +177,8 @@ class NurtureAlgTest extends CatsEffectSuite with Http4sDsl[MockEff] {
       RepoData(
         repo = Repo("scala-steward-org", "scala-steward"),
         cache = dummyRepoCache,
-        config = RepoConfig(
-          pullRequests = PullRequestsConfig(
-            customLabels = customLabels
-          )
-        )
+        config =
+          RepoConfig(pullRequests = PullRequestsConfig(customLabels = customLabels.some).some)
       )
     val update = (dependency %> "3.4.0").single
     val baseBranch = Branch("main")
diff --git a/modules/core/src/test/scala/org/scalasteward/core/repoconfig/RepoConfigAlgTest.scala b/modules/core/src/test/scala/org/scalasteward/core/repoconfig/RepoConfigAlgTest.scala
index b63b789fe5..afbbb018f3 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/repoconfig/RepoConfigAlgTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/repoconfig/RepoConfigAlgTest.scala
@@ -110,10 +110,10 @@ class RepoConfigAlgTest extends FunSuite {
               PullRequestUpdateFilter("*".some).getOrElse(fail("Should not be called"))
             )
           )
-        )
-      ),
+        ).some
+      ).some,
       updates = UpdatesConfig(
-        allow = List(UpdatePattern("eu.timepit".g, None, None)),
+        allow = List(UpdatePattern("eu.timepit".g, None, None)).some,
         pin = List(
           UpdatePattern("eu.timepit".g, Some("refined.1"), Some(VersionPattern(Some("0.8.")))),
           UpdatePattern("eu.timepit".g, Some("refined.2"), Some(VersionPattern(Some("0.8.")))),
@@ -127,15 +127,15 @@ class RepoConfigAlgTest extends FunSuite {
             Some("refined.4"),
             Some(VersionPattern(Some("0.8."), Some("jre")))
           )
-        ),
-        ignore = List(UpdatePattern("org.acme".g, None, Some(VersionPattern(Some("1.0"))))),
-        allowPreReleases = List(UpdatePattern("eu.timepit".g, None, None)),
+        ).some,
+        ignore = List(UpdatePattern("org.acme".g, None, Some(VersionPattern(Some("1.0"))))).some,
+        allowPreReleases = List(UpdatePattern("eu.timepit".g, None, None)).some,
         limit = Some(NonNegInt.unsafeFrom(4)),
         fileExtensions = Some(List(".txt"))
-      ),
+      ).some,
       commits = CommitsConfig(
         message = Some("Update ${artifactName} from ${currentVersion} to ${nextVersion}")
-      ),
+      ).some,
       buildRoots = Some(List(BuildRootConfig.repoRoot, BuildRootConfig("subfolder/subfolder"))),
       dependencyOverrides = List(
         GroupRepoConfig(
@@ -160,9 +160,9 @@ class RepoConfigAlgTest extends FunSuite {
             frequency = Some(PullRequestFrequency.Timespan(7.days))
           )
         )
-      ),
-      assignees = List("scala.steward"),
-      reviewers = List("scala.steward")
+      ).some,
+      assignees = List("scala.steward").some,
+      reviewers = List("scala.steward").some
     )
     assertEquals(obtained, expected)
   }
@@ -213,7 +213,9 @@ class RepoConfigAlgTest extends FunSuite {
     val content = """pullRequests.frequency = "@asap" """
     val config = RepoConfigAlg.parseRepoConfig(content)
     val expected =
-      RepoConfig(pullRequests = PullRequestsConfig(frequency = Some(PullRequestFrequency.Asap)))
+      RepoConfig(pullRequests =
+        PullRequestsConfig(frequency = Some(PullRequestFrequency.Asap)).some
+      )
     assertEquals(config, Right(expected))
   }
 
@@ -221,7 +223,7 @@ class RepoConfigAlgTest extends FunSuite {
     val content = """pullRequests.frequency = "@daily" """
     val config = RepoConfigAlg.parseRepoConfig(content)
     val expected = RepoConfig(pullRequests =
-      PullRequestsConfig(frequency = Some(PullRequestFrequency.Timespan(1.day)))
+      PullRequestsConfig(frequency = Some(PullRequestFrequency.Timespan(1.day))).some
     )
     assertEquals(config, Right(expected))
   }
@@ -230,7 +232,7 @@ class RepoConfigAlgTest extends FunSuite {
     val content = """pullRequests.frequency = "@monthly" """
     val config = RepoConfigAlg.parseRepoConfig(content)
     val expected = RepoConfig(pullRequests =
-      PullRequestsConfig(frequency = Some(PullRequestFrequency.Timespan(30.days)))
+      PullRequestsConfig(frequency = Some(PullRequestFrequency.Timespan(30.days))).some
     )
     assertEquals(config, Right(expected))
   }
@@ -238,7 +240,7 @@ class RepoConfigAlgTest extends FunSuite {
   test("config with 'scalafmt.runAfterUpgrading = true'") {
     val content = "scalafmt.runAfterUpgrading = true"
     val config = RepoConfigAlg.parseRepoConfig(content)
-    val expected = RepoConfig(scalafmt = ScalafmtConfig(runAfterUpgrading = Some(true)))
+    val expected = RepoConfig(scalafmt = ScalafmtConfig(runAfterUpgrading = Some(true)).some)
     assertEquals(config, Right(expected))
   }
 
@@ -343,8 +345,9 @@ class RepoConfigAlgTest extends FunSuite {
     val config = RepoConfigAlg
       .parseRepoConfig(RepoConfigAlg.configToIgnoreFurtherUpdates(update))
       .getOrElse(RepoConfig())
-    val expected =
-      RepoConfig(updates = UpdatesConfig(ignore = List(UpdatePattern("a".g, Some("b"), None))))
+    val expected = RepoConfig(updates =
+      UpdatesConfig(ignore = List(UpdatePattern("a".g, Some("b"), None)).some).some
+    )
     assertEquals(config, expected)
   }
 
@@ -354,7 +357,7 @@ class RepoConfigAlgTest extends FunSuite {
       .parseRepoConfig(RepoConfigAlg.configToIgnoreFurtherUpdates(update))
       .getOrElse(RepoConfig())
     val expected =
-      RepoConfig(updates = UpdatesConfig(ignore = List(UpdatePattern("a".g, None, None))))
+      RepoConfig(updates = UpdatesConfig(ignore = List(UpdatePattern("a".g, None, None)).some).some)
     assertEquals(config, expected)
   }
 
@@ -370,8 +373,8 @@ class RepoConfigAlgTest extends FunSuite {
         List(
           UpdatePattern(groupId = "a".g, artifactId = "b".some, None),
           UpdatePattern(groupId = "c".g, artifactId = "d".some, None)
-        )
-      )
+        ).some
+      ).some
     )
     assertEquals(config, expected)
   }
diff --git a/modules/core/src/test/scala/org/scalasteward/core/repoconfig/RepoConfigLoaderTest.scala b/modules/core/src/test/scala/org/scalasteward/core/repoconfig/RepoConfigLoaderTest.scala
index fd3ce988a6..b3f11f6261 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/repoconfig/RepoConfigLoaderTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/repoconfig/RepoConfigLoaderTest.scala
@@ -37,6 +37,9 @@ class RepoConfigLoaderTest extends FunSuite {
       .unsafeRunSync()
       .getOrElse(None)
     assert(clue(repoConfig).isDefined)
-    assertEquals(repoConfig.get.updates.pin.head.version, Some(VersionPattern(Some("3.4."))))
+    assertEquals(
+      repoConfig.get.updatesOrDefault.pinOrDefault.head.version,
+      Some(VersionPattern(Some("3.4.")))
+    )
   }
 }
diff --git a/modules/core/src/test/scala/org/scalasteward/core/repoconfig/UpdatesConfigTest.scala b/modules/core/src/test/scala/org/scalasteward/core/repoconfig/UpdatesConfigTest.scala
index 3c35d8de1f..0f491c6a65 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/repoconfig/UpdatesConfigTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/repoconfig/UpdatesConfigTest.scala
@@ -1,6 +1,7 @@
 package org.scalasteward.core.repoconfig
 
 import cats.kernel.laws.discipline.MonoidTests
+import cats.syntax.all._
 import munit.DisciplineSuite
 import org.scalasteward.core.TestInstances._
 import org.scalasteward.core.data.GroupId
@@ -23,15 +24,15 @@ class UpdatesConfigTest extends DisciplineSuite {
   private val b00 = UpdatePattern(groupIdB, None, None)
 
   test("mergePin: basic checks") {
-    assertEquals(UpdatesConfig.mergePin(Nil, Nil), Nil)
-    assertEquals(UpdatesConfig.mergePin(List(a00), Nil), List(a00))
-    assertEquals(UpdatesConfig.mergePin(Nil, List(b00)), List(b00))
-    assertEquals(UpdatesConfig.mergePin(List(a00), List(b00)), List(a00, b00))
+    assertEquals(UpdatesConfig.mergePin(Nil.some, Nil.some), Nil.some)
+    assertEquals(UpdatesConfig.mergePin(List(a00).some, Nil.some), List(a00).some)
+    assertEquals(UpdatesConfig.mergePin(Nil.some, List(b00).some), List(b00).some)
+    assertEquals(UpdatesConfig.mergePin(List(a00).some, List(b00).some), List(a00, b00).some)
 
-    assertEquals(UpdatesConfig.mergePin(List(aa1), List(aa1, ac3)), List(aa1, ac3))
+    assertEquals(UpdatesConfig.mergePin(List(aa1).some, List(aa1, ac3).some), List(aa1, ac3).some)
 
-    assertEquals(UpdatesConfig.mergePin(List(aa1), List(aa2)), List(aa2))
-    assertEquals(UpdatesConfig.mergePin(List(aa2), List(aa1)), List(aa1))
+    assertEquals(UpdatesConfig.mergePin(List(aa1).some, List(aa2).some), List(aa2).some)
+    assertEquals(UpdatesConfig.mergePin(List(aa2).some, List(aa1).some), List(aa1).some)
   }
 
   test("mergePin: scala 3 LTS") {
@@ -45,7 +46,7 @@ class UpdatesConfigTest extends DisciplineSuite {
         default: List[UpdatePattern],
         local: List[UpdatePattern]
     ): List[UpdatePattern] =
-      UpdatesConfig.mergePin(default, local)
+      UpdatesConfig.mergePin(default.some, local.some).getOrElse(Nil)
 
     assertEquals(mergeDefaultWithLocal(default = List(s33), local = Nil), List(s33))
     assertEquals(mergeDefaultWithLocal(default = List(s33), local = List(s34)), List(s34))
@@ -58,40 +59,58 @@ class UpdatesConfigTest extends DisciplineSuite {
   }
 
   test("mergeAllow: basic checks") {
-    assertEquals(UpdatesConfig.mergeAllow(Nil, Nil), Nil)
-    assertEquals(UpdatesConfig.mergeAllow(List(a00), Nil), List(a00))
-    assertEquals(UpdatesConfig.mergeAllow(Nil, List(a00)), List(a00))
+    assertEquals(UpdatesConfig.mergeAllow(Nil.some, Nil.some), Nil.some)
+    assertEquals(UpdatesConfig.mergeAllow(List(a00).some, Nil.some), List(a00).some)
+    assertEquals(UpdatesConfig.mergeAllow(Nil.some, List(a00).some), List(a00).some)
 
-    assertEquals(UpdatesConfig.mergeAllow(List(a00), List(a00)), List(a00))
+    assertEquals(UpdatesConfig.mergeAllow(List(a00).some, List(a00).some), List(a00).some)
     assertEquals(
-      UpdatesConfig.mergeAllow(List(a00), List(b00)),
-      UpdatesConfig.nonExistingUpdatePattern
+      UpdatesConfig.mergeAllow(List(a00).some, List(b00).some),
+      UpdatesConfig.nonExistingUpdatePattern.some
     )
 
-    assertEquals(UpdatesConfig.mergeAllow(List(a00), List(aa1, ab0, ac3)), List(aa1, ab0, ac3))
-    assertEquals(UpdatesConfig.mergeAllow(List(aa1, ab0, ac3), List(a00)), List(aa1, ab0, ac3))
+    assertEquals(
+      UpdatesConfig.mergeAllow(List(a00).some, List(aa1, ab0, ac3).some),
+      List(aa1, ab0, ac3).some
+    )
+    assertEquals(
+      UpdatesConfig.mergeAllow(List(aa1, ab0, ac3).some, List(a00).some),
+      List(aa1, ab0, ac3).some
+    )
 
-    assertEquals(UpdatesConfig.mergeAllow(List(aa0), List(aa1, aa2)), List(aa1, aa2))
-    assertEquals(UpdatesConfig.mergeAllow(List(aa1, aa2), List(aa0)), List(aa1, aa2))
+    assertEquals(UpdatesConfig.mergeAllow(List(aa0).some, List(aa1, aa2).some), List(aa1, aa2).some)
+    assertEquals(UpdatesConfig.mergeAllow(List(aa1, aa2).some, List(aa0).some), List(aa1, aa2).some)
 
-    assertEquals(UpdatesConfig.mergeAllow(List(aa0), List(aa0, ab0)), List(aa0))
-    assertEquals(UpdatesConfig.mergeAllow(List(aa0, ab0), List(aa0, ab0)), List(aa0, ab0))
+    assertEquals(UpdatesConfig.mergeAllow(List(aa0).some, List(aa0, ab0).some), List(aa0).some)
+    assertEquals(
+      UpdatesConfig.mergeAllow(List(aa0, ab0).some, List(aa0, ab0).some),
+      List(aa0, ab0).some
+    )
 
-    assertEquals(UpdatesConfig.mergeAllow(List(aa1), List(aa1)), List(aa1))
+    assertEquals(UpdatesConfig.mergeAllow(List(aa1).some, List(aa1).some), List(aa1).some)
     assertEquals(
-      UpdatesConfig.mergeAllow(List(aa1), List(aa2)),
-      UpdatesConfig.nonExistingUpdatePattern
+      UpdatesConfig.mergeAllow(List(aa1).some, List(aa2).some),
+      UpdatesConfig.nonExistingUpdatePattern.some
     )
-    assertEquals(UpdatesConfig.mergeAllow(List(aa1, ab0, ac0), List(aa2, ac0)), List(ac0))
-    assertEquals(UpdatesConfig.mergeAllow(List(aa1, aa2), List(aa1, aa2)), List(aa1, aa2))
-    assertEquals(UpdatesConfig.mergeAllow(List(aa1, aa2), List(aa1, ac3)), List(aa1))
+    assertEquals(
+      UpdatesConfig.mergeAllow(List(aa1, ab0, ac0).some, List(aa2, ac0).some),
+      List(ac0).some
+    )
+    assertEquals(
+      UpdatesConfig.mergeAllow(List(aa1, aa2).some, List(aa1, aa2).some),
+      List(aa1, aa2).some
+    )
+    assertEquals(UpdatesConfig.mergeAllow(List(aa1, aa2).some, List(aa1, ac3).some), List(aa1).some)
   }
 
   test("mergeIgnore: basic checks") {
-    assertEquals(UpdatesConfig.mergeIgnore(Nil, Nil), Nil)
-    assertEquals(UpdatesConfig.mergeIgnore(List(a00), Nil), List(a00))
-    assertEquals(UpdatesConfig.mergeIgnore(Nil, List(b00)), List(b00))
-    assertEquals(UpdatesConfig.mergeIgnore(List(aa1, b00), List(aa1, aa2)), List(aa1, b00, aa2))
+    assertEquals(UpdatesConfig.mergeIgnore(Some(Nil), Some(Nil)), Some(Nil))
+    assertEquals(UpdatesConfig.mergeIgnore(Some(List(a00)), Some(Nil)), Some(List(a00)))
+    assertEquals(UpdatesConfig.mergeIgnore(Some(Nil), Some(List(b00))), Some(List(b00)))
+    assertEquals(
+      UpdatesConfig.mergeIgnore(Some(List(aa1, b00)), Some(List(aa1, aa2))),
+      Some(List(aa1, b00, aa2))
+    )
   }
 
   test("mergeFileExtensions: basic checks") {
diff --git a/modules/core/src/test/scala/org/scalasteward/core/update/FilterAlgTest.scala b/modules/core/src/test/scala/org/scalasteward/core/update/FilterAlgTest.scala
index c3065f4de7..ba9b4a3ab4 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/update/FilterAlgTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/update/FilterAlgTest.scala
@@ -52,10 +52,11 @@ class FilterAlgTest extends FunSuite {
 
   test("localFilter: allowed update to pre-releases of a different series") {
     val update = ("com.jsuereth".g % "sbt-pgp".a % "1.1.2-1" %> Nel.of("2.0.1-M3")).single
-    val allowedPreReleases =
-      UpdatePattern("com.jsuereth".g, Some("sbt-pgp"), None) :: config.updates.allowPreReleases
-    val configWithAllowed =
-      config.copy(updates = config.updates.copy(allowPreReleases = allowedPreReleases))
+    val allowedPreReleases = UpdatePattern("com.jsuereth".g, Some("sbt-pgp"), None) ::
+      config.updatesOrDefault.allowPreReleasesOrDefault
+    val configWithAllowed = config.copy(updates =
+      config.updatesOrDefault.copy(allowPreReleases = allowedPreReleases.some).some
+    )
 
     val expected = Right(update.copy(newerVersions = Nel.of("2.0.1-M3".v)))
     assertEquals(localFilter(update, configWithAllowed), expected)
@@ -64,7 +65,9 @@ class FilterAlgTest extends FunSuite {
   test("ignore update via config updates.ignore") {
     val update = ("eu.timepit".g % "refined".a % "0.8.0" %> "0.8.1").single
     val config = RepoConfig(updates =
-      UpdatesConfig(ignore = List(UpdatePattern(GroupId("eu.timepit"), Some("refined"), None)))
+      UpdatesConfig(ignore =
+        List(UpdatePattern(GroupId("eu.timepit"), Some("refined"), None)).some
+      ).some
     )
 
     val initialState = MockState.empty
@@ -89,8 +92,8 @@ class FilterAlgTest extends FunSuite {
             Some("scala-compiler"),
             Some(VersionPattern(exact = Some("2.13.8")))
           )
-        )
-      )
+        ).some
+      ).some
     )
     val expected = Right(update.copy(newerVersions = Nel.of("2.13.7".v)))
     assertEquals(localFilter(update, config), expected)
@@ -109,8 +112,8 @@ class FilterAlgTest extends FunSuite {
             Some("refined"),
             Some(VersionPattern(Some("0.8")))
           )
-        )
-      )
+        ).some
+      ).some
     )
 
     val filtered1 = filterAlg
@@ -146,8 +149,8 @@ class FilterAlgTest extends FunSuite {
           UpdatePattern(GroupId("org.my1"), None, Some(VersionPattern(Some("0.8")))),
           UpdatePattern(GroupId("org.my2"), None, None),
           UpdatePattern(GroupId("org.my3"), Some("artifact"), None)
-        )
-      )
+        ).some
+      ).some
     )
 
     included.foreach { update =>
@@ -180,8 +183,8 @@ class FilterAlgTest extends FunSuite {
             Some(update.artifactId.name),
             Some(VersionPattern(suffix = Some("jre8")))
           )
-        )
-      )
+        ).some
+      ).some
     )
 
     val filtered = localFilter(update, config)
@@ -200,8 +203,8 @@ class FilterAlgTest extends FunSuite {
             Some(update.artifactId.name),
             Some(VersionPattern(suffix = Some("jre11")))
           )
-        )
-      )
+        ).some
+      ).some
     )
 
     val filtered = localFilter(update, config)
@@ -220,8 +223,8 @@ class FilterAlgTest extends FunSuite {
             Some(update.artifactId.name),
             Some(VersionPattern(Some("7.2."), Some("jre8")))
           )
-        )
-      )
+        ).some
+      ).some
     )
 
     assertEquals(localFilter(update, config), Left(VersionPinnedByConfig(update)))
diff --git a/modules/core/src/test/scala/org/scalasteward/core/update/PruningAlgTest.scala b/modules/core/src/test/scala/org/scalasteward/core/update/PruningAlgTest.scala
index 5b5e2066db..1e69473aee 100644
--- a/modules/core/src/test/scala/org/scalasteward/core/update/PruningAlgTest.scala
+++ b/modules/core/src/test/scala/org/scalasteward/core/update/PruningAlgTest.scala
@@ -191,7 +191,7 @@ class PruningAlgTest extends FunSuite {
             DependencyInfo("org.scala-lang".g % "scala-library".a % "2.12.14", List("build.sbt")),
             DependencyInfo("org.scala-lang".g % "scala-library".a % "2.13.5", List("build.sbt"))
           ),
-          List(MavenRepository("public", "https://repo5.org/maven/", None, Nil))
+          List(MavenRepository("public", "https://repo5.org/maven/", None, None))
         )
       )
     )
diff --git a/project/Dependencies.scala b/project/Dependencies.scala
index 73498b413e..2aaa0e6776 100644
--- a/project/Dependencies.scala
+++ b/project/Dependencies.scala
@@ -9,7 +9,6 @@ object Dependencies {
   val catsParse = "org.typelevel" %% "cats-parse" % "1.1.0"
   val circeConfig = "io.circe" %% "circe-config" % "0.10.1"
   val circeGeneric = "io.circe" %% "circe-generic" % "0.14.10"
-  val circeGenericExtras = "io.circe" %% "circe-generic-extras" % "0.14.4"
   val circeLiteral = "io.circe" %% "circe-literal" % circeGeneric.revision
   val circeParser = "io.circe" %% "circe-parser" % circeGeneric.revision
   val circeRefined = "io.circe" %% "circe-refined" % "0.15.1"
@@ -33,7 +32,7 @@ object Dependencies {
   val jjwtApi = "io.jsonwebtoken" % "jjwt-api" % "0.12.6"
   val jjwtImpl = "io.jsonwebtoken" % "jjwt-impl" % jjwtApi.revision
   val jjwtJackson = "io.jsonwebtoken" % "jjwt-jackson" % jjwtApi.revision
-  val millMain = "com.lihaoyi" % "mill-main_2.13" % "0.12.4"
+  val millMain = "com.lihaoyi" % "mill-main_2.13" % "0.12.5"
   val monocleCore = "dev.optics" %% "monocle-core" % "3.3.0"
   val munit = "org.scalameta" %% "munit" % "1.0.3"
   val munitCatsEffect = "org.typelevel" %% "munit-cats-effect" % "2.0.0"