diff --git a/org.jhotdraw8.icollection/src/main/java/org.jhotdraw8.icollection/org/jhotdraw8/icollection/ChampSet.java b/org.jhotdraw8.icollection/src/main/java/org.jhotdraw8.icollection/org/jhotdraw8/icollection/ChampSet.java
index 30414aaed..3831a9e0e 100644
--- a/org.jhotdraw8.icollection/src/main/java/org.jhotdraw8.icollection/org/jhotdraw8/icollection/ChampSet.java
+++ b/org.jhotdraw8.icollection/src/main/java/org.jhotdraw8.icollection/org/jhotdraw8/icollection/ChampSet.java
@@ -201,6 +201,9 @@ public ChampSet<E> add(@Nullable E element) {
     @Override
     @SuppressWarnings("unchecked")
     public ChampSet<E> addAll(Iterable<? extends E> c) {
+        if(isEmpty()&&c instanceof ChampSet<? extends E> s){
+            return (ChampSet<E>) s;
+        }
         var m = toMutable();
         return m.addAll(c) ? m.toImmutable() : this;
     }
diff --git a/org.jhotdraw8.icollection/src/main/java/org.jhotdraw8.icollection/org/jhotdraw8/icollection/ChampVectorSet.java b/org.jhotdraw8.icollection/src/main/java/org.jhotdraw8.icollection/org/jhotdraw8/icollection/ChampVectorSet.java
index c43effcb3..1491fa3f0 100644
--- a/org.jhotdraw8.icollection/src/main/java/org.jhotdraw8.icollection/org/jhotdraw8/icollection/ChampVectorSet.java
+++ b/org.jhotdraw8.icollection/src/main/java/org.jhotdraw8.icollection/org/jhotdraw8/icollection/ChampVectorSet.java
@@ -245,6 +245,9 @@ public ChampVectorSet<E> add(@Nullable E key) {
     @Override
     @SuppressWarnings({"unchecked"})
     public ChampVectorSet<E> addAll(Iterable<? extends E> c) {
+        if(isEmpty()&&c instanceof ChampVectorSet<? extends E> s){
+            return (ChampVectorSet<E>) s;
+        }
         var m = toMutable();
         return m.addAll(c) ? m.toImmutable() : this;
     }
diff --git a/pom.xml b/pom.xml
index a5f7100da..3fb2b79c4 100644
--- a/pom.xml
+++ b/pom.xml
@@ -386,12 +386,6 @@
         <version>1.37</version>
         <scope>test</scope>
       </dependency>
-      <dependency>
-        <groupId>org.openjdk.jmh</groupId>
-        <artifactId>jmh-generator-annprocess</artifactId>
-        <version>1.37</version>
-        <scope>test</scope>
-      </dependency>
       <!-- https://mvnrepository.com/artifact/org.jspecify/jspecify -->
       <dependency>
         <groupId>org.jspecify</groupId>