Use default state serializer content type if state is not null (#1033)

Signed-off-by: Antonio Sanchez <antonio.maria.sanchez@gmail.com>
Co-authored-by: Cassie Coyle <cassie@diagrid.io>

sdk/src/main/java/io/dapr/client/AbstractDaprClient.java

@@ -493,7 +493,11 @@ public Mono<Void> saveState(String storeName, String key, Object value) {
    */
   @Override
   public Mono<Void> saveState(String storeName, String key, String etag, Object value, StateOptions options) {
-    State<?> state = new State<>(key, value, etag, options);
+    Map<String, String> meta = null;
+    if (value != null) {
+      meta = Collections.singletonMap("contentType", stateSerializer.getContentType());
+    }
+    State<?> state = new State<>(key, value, etag, meta, options);
     return this.saveBulkState(storeName, Collections.singletonList(state));
   }