SocketIO -sendAcknowledgement:withArgs: with nil args causes a crash

[thepatrick]

Except the crash is from the call to NSJSONSerialization dataWithJSONObject - it'd be great if -sendAcknowledgement:withArgs: either did:

• raise an exception/assert on nil itself (to make it much easier to find the error!)
• work anyway (e.g. by defaulting the args to @[])