Github user MikeThomsen commented on the issue:
https://github.com/apache/nifi/pull/2749
@markap14 can you review? Since you brought this up on the dev list, here's
the simple summary:
The test framework is too strict on processors where input is optional. In
those cases, it's common to just call `evaluateExpressionLanguage` with a null
flowfile, but the test framework won't allow that. So it reports false
negatives on execution that would go through with live execution of the
processors.---
