NIFI-4798 allow empty value for UpdateAttribute property

[markobean]

Summary

There exists a validator for dynamic properties added to UpdateAttribute. This prevents the "Set empty string" checkbox from being used; it results in an invalid property. Removed the validator to allow more freedom in assigning attribute values for UpdateAttribute processor.

NIFI-4798

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[joewitt]

What is the intended outcome @markobean ? Is this because someone wants to wipe out an attribute value to empty string?

[markobean]

Yes, the goal is to be able to have an attribute exist with no value (empty string) on a given flowfile. Honestly, I'm not sure how much this is used in production, but could be useful in debugging flows.

[NissimShiman]

Very nice addition @markobean !

I've bumped into this issue a few times myself when setting up tests (i.e. not being able to set an empty value value for an attribute), but never followed up further, so thank you for the jira and PR!

Clean code and unit test.

Compiled code and tested with both a new attribute with an empty value as well as an existing attribute with an empty value (i.e. to replace value of existing attribute with an empty value) and both worked fine.

Thanks!

LGTM +1

[mattyb149]

Reviewing...

[mattyb149]

+1 LGTM, verified the intended behavior. Thanks for the fix! Merging to main

[markobean]

Thanks @mattyb149 !