I think this change will let AionBlockChainImpl.isValid() throw null exception. Please have a check.

I updated the null check in AionBlockchainImpl.isValid to exit if the parent block is null.

Cool.

Will let AionBlockChainImpl.createNewMiningBlockInternal() throw NPE

It would already throw an NPE because the blockFamily is accessed without a null check. The reason for the NPE differs but it will be thown in either case. If that happens I think we should allows the failure and fix the cause when we find one.

So We should just throw NPE if the input hash equal to null. instead of return values (or return null)

Same as the other method.

Ok. I made the update.