HDFS-17098. DatanodeManager does not handle null storage type properly. (#6840). Contributed by ConfX.

Signed-off-by: Shilun Fan <slfan1989@apache.org>

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeManager.java

@@ -678,7 +678,15 @@ public class DatanodeManager {
     Consumer<List<DatanodeInfoWithStorage>> secondarySort = null;
     if (readConsiderStorageType) {
       Comparator<DatanodeInfoWithStorage> comp =
-          Comparator.comparing(DatanodeInfoWithStorage::getStorageType);
+          Comparator.comparing(DatanodeInfoWithStorage::getStorageType, (s1, s2) -> {
+            if (s1 == null) {
+              return (s2 == null) ? 0 : -1;
+            } else if (s2 == null) {
+              return 1;
+            } else {
+              return s2.compareTo(s1);
+            }
+          });
       secondarySort = list -> Collections.sort(list, comp);
     }
     if (readConsiderLoad) {