added consideration for cases where the value wrapped by value class is null

Author: k163377

src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinAnnotationIntrospector.kt

@@ -94,6 +94,9 @@ internal class KotlinAnnotationIntrospector(private val context: Module.SetupCon
         else -> null
     }
 
+    // Perform proper serialization even if the value wrapped by the value class is null.
+    override fun findNullSerializer(am: Annotated) = findSerializer(am)
+
     /**
      * Subclasses can be detected automatically for sealed classes, since all possible subclasses are known
      * at compile-time to Kotlin. This makes [com.fasterxml.jackson.annotation.JsonSubTypes] redundant.

src/main/kotlin/com/fasterxml/jackson/module/kotlin/KotlinSerializers.kt

@@ -82,7 +82,7 @@ internal class ValueClassBoxSerializer(
 ) : StdSerializer<Any>(outerClazz.java) {
     private val boxMethod = _handledType.getMethod("box-impl", innerClazz)
 
-    override fun serialize(value: Any, gen: JsonGenerator, provider: SerializerProvider) {
+    override fun serialize(value: Any?, gen: JsonGenerator, provider: SerializerProvider) {
         // Values retrieved from getter are considered validated and constructor-impl is not executed.
         val boxed = boxMethod.invoke(null, value)