Allow for zero IDs; notifications are only NULL #94
Description
From @bradjones1
If a client sends a request with ID -0- (zero) this is converted into a response with ID null, as the check for the presence of an ID in the ResponseCreator is not sufficiently typesafe. The perils of working in PHP, I guess!
I was getting errors on the client side like Received a surprise response from the server with id null after sending such a request ID.