Restrict extension setter and getter operations to non-nullable T

java/kotlin/src/main/kotlin/com/google/protobuf/ExtendableMessageExtensions.kt

@@ -7,7 +7,7 @@ import com.google.protobuf.GeneratedMessageV3
 operator fun <
   M : GeneratedMessageV3.ExtendableMessage<M>,
   B : GeneratedMessageV3.ExtendableBuilder<M, B>,
-  T
+  T : Any
   > B.set(extension: ExtensionLite<M, T>, value: T) {
   setExtension(extension, value)
 }
@@ -16,7 +16,7 @@ operator fun <
 operator fun <
   M : GeneratedMessageV3.ExtendableMessage<M>,
   MorBT : GeneratedMessageV3.ExtendableMessageOrBuilder<M>,
-  T
+  T : Any
   > MorBT.get(extension: ExtensionLite<M, T>): T = getExtension(extension)
 
 /** Returns true if the specified extension is set on this builder. */

java/kotlin/src/main/kotlin/com/google/protobuf/ExtendableMessageLiteExtensions.kt

@@ -7,14 +7,14 @@ import com.google.protobuf.GeneratedMessageLite
 operator fun <
   M : GeneratedMessageLite.ExtendableMessage<M, *>,
   MOrBT : GeneratedMessageLite.ExtendableMessageOrBuilder<M, *>,
-  T
+  T : Any
   > MOrBT.get(extension: ExtensionLite<M, T>): T = getExtension(extension)
 
 /** Sets the current value of the proto extension in this builder. */
 operator fun <
   M : GeneratedMessageLite.ExtendableMessage<M, B>,
   B : GeneratedMessageLite.ExtendableBuilder<M, B>,
-  T
+  T : Any
   > B.set(extension: ExtensionLite<M, T>, value: T) {
   setExtension(extension, value)
 }