No class 'com.sun.proxy.$Proxy33' was registered - BadRequest on GAE endpoints

Question

All of the sudden, previously working Google App Engine (JAVA) endpoint started to throw this at me:

com.google.api.client.googleapis.json.GoogleJsonResponseException: 400 Bad Request
{
  "code" : 400,
  "errors" : [ {
    "domain" : "global",
    "message" : "java.lang.IllegalArgumentException: No class 'com.sun.proxy.$Proxy33' was registered",
    "reason" : "badRequest"
  } ],
  "message" : "java.lang.IllegalArgumentException: No class 'com.sun.proxy.$Proxy33' was registered"
}

I'm executing endpoint method from android app like this:

CollectionResponseRPlayer response = endpoint.checkResult(gameId, answer, hash).execute();

gameId is Long, and the answer and hash are Strings

I stopped on execute() line to preview what values are passed in gameId, answer and hash to figure why could it be the bad request. They are as follows:

gameId = 8113932860298394396
answer = "KCMR"
hash = "D3C04148ACD9A166E6DBD0268D76AC39CB6C7CEB4B056522522B3551EA28830AFGF129DD89AB4CD6F7375526C796DE031450DF32611ACA1FEB904AB4ECCC3D7CD15CB267F38F10BAE1951RTBBDD3EC110005D67ED82FC5C8EF4E74FF5363D858AFCCAE4EF0A078FB550E833FD527B54"

As you can see, hash field is pretty long one. Could it be the reason? I don't think it is. String in GAE is limited to 500 chars, and this hash barely 250. Also, I use the very same hash in every enpoint in may app, and this is the only one causing trouble...

Answer 1

I'm using Objectify. Problem was caused by:

ofy().save().entities(players, user);

Obviously I cannot provide collection and single entity at once, sot I fixed it with:

    ofy().save().entities(players);
    ofy().save().entity(user);