Github user mattyb149 commented on the issue:
https://github.com/apache/nifi/pull/2101
By setting the NON_BLANK or NON_EMPTY validator, you are prohibiting
someone from using an empty string as a username or password, which is what you
want, right? So that unit test should fail because you are setting an empty
string on USERNAME and then asserting that it is valid, when it is not.---
