Github user alopresto commented on the issue:
https://github.com/apache/nifi/pull/2959
As discovered by @bbende , I introduced a bug in my commit
[f60585a](https://github.com/apache/nifi/commit/f60585a9b6df6b3b28be1eb80a0a60deac6c0493#diff-882d0904bb315ac8a455aec69e6d44d8)
as part of [PR 2841](https://github.com/apache/nifi/pull/2841) for
[NIFI-5376](https://issues.apache.org/jira/browse/NIFI-5376) which stops
cluster startup if no `nifi.sensitive.props.key` value is entered in
`nifi.properties`. Previously, a default static value is used (all docs
indicate this should *not* be relied on and a custom, unique value should be
provided at deployment time), but this is an unintentional regression and was
not documented.
This fix prints a warning to the log if no value is provided but restores
the previous functionality of using the default.
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