CASSANDRA-21128: CompactionManager.submitMaximal crash due to node restart race condition

[teamconfx]

This PR fix CASSANDRA-21128.

Issue

CompactionManager.submitMaximal() threw a NullPointerException when calling tasks.isEmpty() because getMaximalTasks() can return null during node restart scenarios (when there are uninterruptible compactions).

Fix Applied

File: src/java/org/apache/cassandra/db/compaction/CompactionManager.java:1179

Changed:

  if (tasks.isEmpty())

To:

  if (tasks == null || tasks.isEmpty())

Test Added

File: test/unit/org/apache/cassandra/db/compaction/CompactionManagerSubmitMaximalTest.java

Two test cases:

1. testSubmitMaximalHandlesNullTasks() - Uses Mockito to simulate getMaximalTasks() returning null and verifies the method returns an empty list instead of throwing NPE
2. testSubmitMaximalHandlesEmptyTasks() - Verifies normal behavior with empty compaction tasks