Github user mattyb149 commented on the issue:
https://github.com/apache/nifi/pull/2699
I took the liberty of adding the missing evaluateAttributeExpressions()
call, the unit tests pass at that point but if Expression Language is present,
then we can't count on the File Exists Validator to catch missing schema files.
I added a check for file.exists() and unit tests for valid and invalid (with
EL). Feel free to cherry-pick
https://github.com/mattyb149/nifi/commit/a452382bed64cd4ddda69711e7382829726503ee
into your branch and push back up here for review, or @MikeThomsen if you're
cool with it you could just cherry pick his and my commits from
https://github.com/mattyb149/nifi/tree/NIFI-5192 before merge.
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