[BugFix] Fix get max compaction score NullPointerException bug (backport #63268) (#63276)

Signed-off-by: wyb <wybb86@gmail.com>
Co-authored-by: wyb <wybb86@gmail.com>

Author: mergify[bot]

fe/fe-core/src/main/java/com/starrocks/lake/compaction/CompactionMgr.java

@@ -206,8 +206,8 @@ public PartitionStatistics getStatistics(PartitionIdentifier identifier) {
     }
 
     public double getMaxCompactionScore() {
-        return partitionStatisticsHashMap.values().stream().mapToDouble(stat -> stat.getCompactionScore().getMax())
-                .max().orElse(0);
+        return partitionStatisticsHashMap.values().stream().filter(stat -> stat.getCompactionScore() != null)
+                .mapToDouble(stat -> stat.getCompactionScore().getMax()).max().orElse(0);
     }
 
     void enableCompactionAfter(PartitionIdentifier partition, long delayMs) {

fe/fe-core/src/test/java/com/starrocks/lake/compaction/CompactionMgrTest.java

@@ -166,17 +166,25 @@ public void testGetMaxCompactionScore() {
         PartitionIdentifier partition2 = new PartitionIdentifier(1, 2, 4);
         Assertions.assertEquals(0, compactionMgr.getMaxCompactionScore(), delta);
 
+        // load and compact partition 1
         compactionMgr.handleLoadingFinished(partition1, 2, System.currentTimeMillis(),
                 Quantiles.compute(Lists.newArrayList(1d)));
         Assertions.assertEquals(1, compactionMgr.getMaxCompactionScore(), delta);
         compactionMgr.handleCompactionFinished(partition1, 3, System.currentTimeMillis(),
                 Quantiles.compute(Lists.newArrayList(2d)), 1234, false);
         Assertions.assertEquals(2, compactionMgr.getMaxCompactionScore(), delta);
 
+        // load partition 2
         compactionMgr.handleLoadingFinished(partition2, 2, System.currentTimeMillis(),
                 Quantiles.compute(Lists.newArrayList(3d)));
         Assertions.assertEquals(3, compactionMgr.getMaxCompactionScore(), delta);
 
+        // set partition 2 compaction score to null
+        PartitionStatistics statistics2 = compactionMgr.getStatistics(partition2);
+        statistics2.setCompactionScore(null);
+        Assertions.assertEquals(2, compactionMgr.getMaxCompactionScore(), delta);
+
+        // remove partition 2
         compactionMgr.removePartition(partition2);
         Assertions.assertEquals(2, compactionMgr.getMaxCompactionScore(), delta);
     }