Visual studio 2015 test runner exception: tsqlttestexecutor

I had this error when run all tests in test explorer:

An exception occurred while invoking executor 'executor://tsqlttestexecutor/v1': Object reference not set to an instance of an object.

It can be consistently re-produced:
- if all tests pass, it has no issue
- exec tSQLt.AssertEqualsTable 'expected', 'actual' will cause above error and stop execution of the rest of the tests if expected and actual tables are different for a test.
- if one table is empty, it has no issue

Hope this will help.

Thanks!