Provide clear error message instead of Null Pointer Exception(NPE)

[longquanzheng]

When workflow type, workflowState, RPC are not registered, what are the errors we are thrown today?

Some of them are NPE which is hard to troubleshoot. We should provide clear message that these entities are not registerd, maybe even provide potential reasons (delete or rename), and how to fix them.

Also similarly:

• data attribute
• search attribute
• Signal channel
• InternalChannel
  What are the behavior when they are used without proper registered?