So where would one obtain a non-null id value and how would they insert that into the client message to the server? Is that the profile name or the account email address?
When a player connects to a server the server checks to see if you have a legit 'id', if they do the player connects otherwise they are kicked. For some reason the server doesn't handle the player having a null 'id' correctly causing a network issue. This is more than likely a result of the 1.7.0 update, as Mojang did a complete multiplayer code overhaul.
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