Fix NPE in LazyPersistFileScrubber. Contributed by Inigo Goiri.

(cherry picked from commit 303c8dc9b6c853c0939ea9ba14388897cc258071)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -3895,9 +3895,13 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
         while (it.hasNext()) {
           Block b = it.next();
           BlockInfo blockInfo = blockManager.getStoredBlock(b);
-          BlockCollection bc = getBlockCollection(blockInfo);
-          if (bc.getStoragePolicyID() == lpPolicy.getId()) {
-            filesToDelete.add(bc);
+          if (blockInfo == null) {
+            LOG.info("Cannot find block info for block " + b);
+          } else {
+            BlockCollection bc = getBlockCollection(blockInfo);
+            if (bc.getStoragePolicyID() == lpPolicy.getId()) {
+              filesToDelete.add(bc);
+            }
           }
         }