Mojang included some sanity checks on arguments passed to the BlockData.
This code results in the Hash look up occuring twice per call, one to test if it exists
and another to retrieve the result.
This code should ideally never be hit, unless mojang released a bad build. We can discover bugs with this as furthur code that never expects a null
would then NPE, so it would not result in hidden issues.
This is super hot code, so removing those checks should give decent gains.
Aikar