NIFI-7223 Fixed TLS regression when key password is set to empty

[alopresto]

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Description of PR

Fixed a regression in the TLS OkHttpClientBuilder configuration if the key password is set to an empty string.

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[joewitt]

in reviewing the actions results on thenatog build it appears this will fail in Java 11 as it is using classes that appear to only exist in the Oracle JDK distribution. We need to eliminate such reliance.

[alopresto]

Working to resolve that issue.

[alopresto]

I don't have push access to @thenatog 's repository so I couldn't update this PR with the fix. Instead I have opened PR 4145 which resolves the issue (and includes all commits here). Please review that moving forward.