Github user pvillard31 commented on the issue:
https://github.com/apache/nifi/pull/2138
I already noticed this error while working on others PRs (I'm a bit
surprised I didn't notice the NPE on this PR...). It's because we're checking
if the processor is valid before enabling expression validation
(https://github.com/apache/nifi/blob/master/nifi-mock/src/main/java/org/apache/nifi/util/StandardProcessorTestRunner.java#L169).
We can't really do it the other way around without changing a lot of things.
I updated the PR to just check if ``expectExpressions`` is null and, if
yes, return false. This way we can use ``isExpressionLanguagePresent()`` in a
custom validate method.
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