Fix error handling for incorrectly set up log based streams

[leslievandemark]

Description of change

The deserializer.deserialize_item will not return None if the incorrect object is passed in, it will throw an AttributeError: 'NoneType' object has no attribute 'items' . This PR fixes the error handling to check if the record contains NewImage before deserializing, to throw the correct actionable error.

Manual QA steps

• tested locally with clients connection

Risks

• low, the tap should not throw an actionable error message if log based is not set up correctly

Rollback steps

• revert this branch