Fix. NPE on async result

Author: sleipnir

src/main/java/io/eigr/spawn/api/Value.java

@@ -157,7 +157,7 @@ public String toString() {
         final StringBuilder sb = new StringBuilder("Value{");
         sb.append("state=").append(state);
         sb.append("checkpoint=").append(checkpoint);
-        sb.append(", value=").append(response);
+        sb.append(", response=").append(response);
         sb.append(", broadcast=").append(broadcast);
         sb.append(", forward=").append(forward);
         sb.append(", pipe=").append(pipe);

src/main/java/io/eigr/spawn/internal/handlers/ActorServiceHandler.java

@@ -92,7 +92,13 @@ private Protocol.ActorInvocationResponse handleRequest(HttpExchange exchange) th
             if (maybeValueResponse.isPresent()) {
                 Value valueResponse = maybeValueResponse.get();
                 Any encodedState = Any.pack(valueResponse.getState());
-                Any encodedValue = Any.pack(valueResponse.getResponse());
+
+                Any encodedValue;
+                if (Objects.isNull(valueResponse.getResponse())){
+                    encodedValue = Any.pack(Protocol.Noop.getDefaultInstance());
+                }else {
+                    encodedValue = Any.pack(valueResponse.getResponse());
+                }
 
                 Protocol.Context updatedContext = Protocol.Context.newBuilder()
                         .setState(encodedState)