NIFI-15584 Fix NPE in DBCPConnectionPool for Dynamic Properties with Null Values

[apanczyk]

Summary

NIFI-15584
DBCPConnectionPool.getConnectionProperties() throws a NullPointerException when a dynamic property value resolves to null.

The method uses Collectors.toMap to collect dynamic properties into a Map<String, String>. The underlying HashMap.merge() does not accept null values, so when either propertyValue.getValue() (sensitive properties) or propertyValue.evaluateAttributeExpressions().getValue() (non-sensitive properties) returns null, the collector throws an NPE.

Tracking

Please complete the following tracking steps prior to pull request creation.

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
• Pull request contains commits signed with a registered key indicating Verified status

Pull Request Formatting

• Pull Request based on current revision of the main branch
• Pull Request refers to a feature branch with one commit containing changes

Verification

Please indicate the verification steps performed prior to pull request creation.

Build

• Build completed using ./mvnw clean install -P contrib-check
  • JDK 21
  • JDK 25

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

[exceptionfactory]

Thanks for finding and correcting this issue @apanczyk! +1 merging