NIFI-14199 Fix Potential NPE in SslContextConfiguration

[exceptionfactory]

Summary

NIFI-14199 Fixes a potential NullPointerException in the framework SslContextConfiguration when either nifi.security.keystoreType or nifi.security.truststoreType are undefined. Returning an empty string as the default value for the property comparison retains the use of String.contentEquals() for PEM Type checking.

Tracking

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Issue Tracking

• Apache NiFi Jira issue created

Pull Request Tracking

• Pull Request title starts with Apache NiFi Jira issue number, such as NIFI-00000
• Pull Request commit message starts with Apache NiFi Jira issue number, as such NIFI-00000

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• Pull Request refers to a feature branch with one commit containing changes

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Build

• Build completed using mvn clean install -P contrib-check
  • JDK 21

Licensing

• New dependencies are compatible with the Apache License 2.0 according to the License Policy
• New dependencies are documented in applicable LICENSE and NOTICE files

Documentation

• Documentation formatting appears as expected in rendered files

[pvillard31]

+1, will merge after checks are green