Update KotlinSerializer.kt

Add handling of null, Void and Object

examples/features/src/main/java/com/github/kagkarlsson/examples/kotlin/KotlinSerializer.kt

@@ -1,25 +1,42 @@
 package com.github.kagkarlsson.examples.kotlin
 
 import com.github.kagkarlsson.scheduler.serializer.Serializer
+import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.KSerializer
 import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.serializer
+import java.nio.charset.Charset
 import java.nio.charset.StandardCharsets
 
+@OptIn(ExperimentalSerializationApi::class)
 class KotlinSerializer : Serializer {
-    val CHARSET = StandardCharsets.UTF_8
+    private val charset: Charset = StandardCharsets.UTF_8
 
-    override fun serialize(data: Any): ByteArray {
+    override fun serialize(data: Any?): ByteArray {
+        if (data == null) {
+            return ByteArray(0)
+        }
         val serializer = serializer(data.javaClass)
-        return Json.encodeToString(serializer, data).toByteArray(CHARSET);
+        return Json.encodeToString(serializer, data).toByteArray(charset);
     }
 
-    override fun <T : Any?> deserialize(clazz: Class<T>, serializedData: ByteArray): T {
+    @Suppress("UNCHECKED_CAST")
+    override fun <T : Any?> deserialize(clazz: Class<T>, serializedData: ByteArray?): T? {
+        if (serializedData == null || clazz == Void::class.java) {
+            return null
+        }
+
+        // If we do not know the class (e.g. java.lang.Object), decode as generic JSON
+        if (clazz == Any::class.java) {
+            return Json.decodeFromString(JsonElement.serializer(), serializedData.decodeToString()) as T
+        }
+
         // Hackish workaround?
         // https://github.com/Kotlin/kotlinx.serialization/issues/1134
         // https://stackoverflow.com/questions/64284767/replace-jackson-with-kotlinx-serialization-in-javalin-framework/64285478#64285478
 
         val deserializer = serializer(clazz) as KSerializer<T>
-        return Json.decodeFromString(deserializer, String(serializedData, CHARSET))
+        return Json.decodeFromString(deserializer, String(serializedData, charset))
     }
 }