NIFI-1923 - AttributesToJson regex property

[pvillard31]

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[mattyb149]

What do you think about supporting Expression Language for this field? You can keep the same validator, although that doesn't allow validation against flow files, just Variable Registry properties and such. You could support regexes from flow file attributes too, but you'd need a new validator and it would recompile each time, which might not be a great idea from a performance perspective.

[pvillard31]

Agree to add EL evaluation against variable registry, system properties, etc. But won't add the evaluation against the flow file as it will impact the performances as you said.

[mattyb149]

+1 LGTM, ran the tests, verified EL is supported (via variables not flow files). Thanks for the improvement! Merging to master