diff --git a/common/src/main/kotlin/com/google/ai/client/generativeai/common/client/Types.kt b/common/src/main/kotlin/com/google/ai/client/generativeai/common/client/Types.kt
index cb2fb478..c8fc3fb6 100644
--- a/common/src/main/kotlin/com/google/ai/client/generativeai/common/client/Types.kt
+++ b/common/src/main/kotlin/com/google/ai/client/generativeai/common/client/Types.kt
@@ -59,6 +59,7 @@ data class Schema(
   val type: String,
   val description: String? = null,
   val format: String? = null,
+  val nullable: Boolean? = false,
   val enum: List<String>? = null,
   val properties: Map<String, Schema>? = null,
   val required: List<String>? = null,
diff --git a/common/src/main/kotlin/com/google/ai/client/generativeai/common/shared/Types.kt b/common/src/main/kotlin/com/google/ai/client/generativeai/common/shared/Types.kt
index 29882560..64e816e2 100644
--- a/common/src/main/kotlin/com/google/ai/client/generativeai/common/shared/Types.kt
+++ b/common/src/main/kotlin/com/google/ai/client/generativeai/common/shared/Types.kt
@@ -59,7 +59,7 @@ data class Content(@EncodeDefault val role: String? = "user", val parts: List<Pa
 
 @Serializable data class FunctionResponse(val name: String, val response: JsonObject)
 
-@Serializable data class FunctionCall(val name: String, val args: Map<String, String>)
+@Serializable data class FunctionCall(val name: String, val args: Map<String, String?>)
 
 @Serializable data class FileDataPart(@SerialName("file_data") val fileData: FileData) : Part
 
diff --git a/common/src/test/java/com/google/ai/client/generativeai/common/UnarySnapshotTests.kt b/common/src/test/java/com/google/ai/client/generativeai/common/UnarySnapshotTests.kt
index a3f8d77f..13ec5428 100644
--- a/common/src/test/java/com/google/ai/client/generativeai/common/UnarySnapshotTests.kt
+++ b/common/src/test/java/com/google/ai/client/generativeai/common/UnarySnapshotTests.kt
@@ -20,6 +20,7 @@ import com.google.ai.client.generativeai.common.server.BlockReason
 import com.google.ai.client.generativeai.common.server.FinishReason
 import com.google.ai.client.generativeai.common.server.HarmProbability
 import com.google.ai.client.generativeai.common.server.HarmSeverity
+import com.google.ai.client.generativeai.common.shared.FunctionCallPart
 import com.google.ai.client.generativeai.common.shared.HarmCategory
 import com.google.ai.client.generativeai.common.shared.TextPart
 import com.google.ai.client.generativeai.common.util.goldenUnaryFile
@@ -301,4 +302,15 @@ internal class UnarySnapshotTests {
         }
       }
     }
+
+  @Test
+  fun `function call contains null param`() =
+    goldenUnaryFile("success-function-call-null.json") {
+      withTimeout(testTimeout) {
+        val response = apiController.generateContent(textGenerateContentRequest("prompt"))
+        val callPart = (response.candidates!!.first().content!!.parts.first() as FunctionCallPart)
+
+        callPart.functionCall.args["season"] shouldBe null
+      }
+    }
 }
diff --git a/common/src/test/resources/golden-files/unary/success-function-call-null.json b/common/src/test/resources/golden-files/unary/success-function-call-null.json
new file mode 100644
index 00000000..14801eef
--- /dev/null
+++ b/common/src/test/resources/golden-files/unary/success-function-call-null.json
@@ -0,0 +1,45 @@
+{
+  "candidates": [
+    {
+      "content": {
+        "parts": [
+          {
+            "functionCall": {
+              "name": "functionName",
+              "args": {
+                "original_title": "String",
+                "season": null
+              }
+            }
+          }
+        ],
+        "role": "model"
+      },
+      "finishReason": "STOP",
+      "index": 0,
+      "safetyRatings": [
+        {
+          "category": "HARM_CATEGORY_HARASSMENT",
+          "probability": "NEGLIGIBLE"
+        },
+        {
+          "category": "HARM_CATEGORY_SEXUALLY_EXPLICIT",
+          "probability": "NEGLIGIBLE"
+        },
+        {
+          "category": "HARM_CATEGORY_DANGEROUS_CONTENT",
+          "probability": "NEGLIGIBLE"
+        },
+        {
+          "category": "HARM_CATEGORY_HATE_SPEECH",
+          "probability": "NEGLIGIBLE"
+        }
+      ]
+    }
+  ],
+  "usageMetadata": {
+    "promptTokenCount": 774,
+    "candidatesTokenCount": 4176,
+    "totalTokenCount": 4950
+  }
+}
diff --git a/generativeai/src/commonMain/kotlin/dev/shreyaspatil/ai/client/generativeai/type/Part.kt b/generativeai/src/commonMain/kotlin/dev/shreyaspatil/ai/client/generativeai/type/Part.kt
index 6dd316e9..ea65e4eb 100644
--- a/generativeai/src/commonMain/kotlin/dev/shreyaspatil/ai/client/generativeai/type/Part.kt
+++ b/generativeai/src/commonMain/kotlin/dev/shreyaspatil/ai/client/generativeai/type/Part.kt
@@ -47,7 +47,7 @@ class FileDataPart(val uri: String, val mimeType: String) : Part
 fun Part.asFileDataPartOrNull(): FileDataPart? = this as? FileDataPart
 
 /** Represents function call name and params received from requests. */
-class FunctionCallPart(val name: String, val args: Map<String, String>) : Part
+class FunctionCallPart(val name: String, val args: Map<String, String?>) : Part
 
 /** Represents function call output to be returned to the model when it requests a function call */
 class FunctionResponsePart(val name: String, val response: JsonObject) : Part
diff --git a/generativeai/src/main/java/com/google/ai/client/generativeai/internal/util/conversions.kt b/generativeai/src/main/java/com/google/ai/client/generativeai/internal/util/conversions.kt
index dadc2611..dfa8c3c0 100644
--- a/generativeai/src/main/java/com/google/ai/client/generativeai/internal/util/conversions.kt
+++ b/generativeai/src/main/java/com/google/ai/client/generativeai/internal/util/conversions.kt
@@ -150,6 +150,7 @@ internal fun FunctionDeclaration.toInternal() =
       properties = getParameters().associate { it.name to it.toInternal() },
       required = getParameters().map { it.name },
       type = "OBJECT",
+      nullable = false,
     ),
   )
 
@@ -158,6 +159,7 @@ internal fun <T> com.google.ai.client.generativeai.type.Schema<T>.toInternal():
     type.name,
     description,
     format,
+    nullable,
     enum,
     properties?.mapValues { it.value.toInternal() },
     required,
diff --git a/generativeai/src/main/java/com/google/ai/client/generativeai/type/FunctionDeclarations.kt b/generativeai/src/main/java/com/google/ai/client/generativeai/type/FunctionDeclarations.kt
index 80569ad7..21d02b08 100644
--- a/generativeai/src/main/java/com/google/ai/client/generativeai/type/FunctionDeclarations.kt
+++ b/generativeai/src/main/java/com/google/ai/client/generativeai/type/FunctionDeclarations.kt
@@ -173,6 +173,7 @@ class Schema<T>(
   val name: String,
   val description: String,
   val format: String? = null,
+  val nullable: Boolean? = null,
   val enum: List<String>? = null,
   val properties: Map<String, Schema<out Any>>? = null,
   val required: List<String>? = null,
@@ -184,19 +185,39 @@ class Schema<T>(
   companion object {
     /** Registers a schema for an integer number */
     fun int(name: String, description: String) =
-      Schema<Long>(name = name, description = description, type = FunctionType.INTEGER)
+      Schema<Long>(
+        name = name,
+        description = description,
+        type = FunctionType.INTEGER,
+        nullable = false,
+      )
 
     /** Registers a schema for a string */
     fun str(name: String, description: String) =
-      Schema<String>(name = name, description = description, type = FunctionType.STRING)
+      Schema<String>(
+        name = name,
+        description = description,
+        type = FunctionType.STRING,
+        nullable = false,
+      )
 
     /** Registers a schema for a boolean */
     fun bool(name: String, description: String) =
-      Schema<Boolean>(name = name, description = description, type = FunctionType.BOOLEAN)
+      Schema<Boolean>(
+        name = name,
+        description = description,
+        type = FunctionType.BOOLEAN,
+        nullable = false,
+      )
 
     /** Registers a schema for a floating point number */
     fun num(name: String, description: String) =
-      Schema<Double>(name = name, description = description, type = FunctionType.NUMBER)
+      Schema<Double>(
+        name = name,
+        description = description,
+        type = FunctionType.NUMBER,
+        nullable = false,
+      )
 
     /**
      * Registers a schema for a complex object. In a function it will be returned as a [JSONObject]
@@ -208,11 +229,17 @@ class Schema<T>(
         type = FunctionType.OBJECT,
         required = contents.map { it.name },
         properties = contents.associateBy { it.name }.toMap(),
+        nullable = false,
       )
 
     /** Registers a schema for an array */
     fun arr(name: String, description: String) =
-      Schema<List<String>>(name = name, description = description, type = FunctionType.ARRAY)
+      Schema<List<String>>(
+        name = name,
+        description = description,
+        type = FunctionType.ARRAY,
+        nullable = false,
+      )
 
     /** Registers a schema for an enum */
     fun enum(name: String, description: String, values: List<String>) =
@@ -222,6 +249,7 @@ class Schema<T>(
         format = "enum",
         enum = values,
         type = FunctionType.STRING,
+        nullable = false,
       )
   }
 }