diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DiskBalancer.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DiskBalancer.java
index 6b2cd52f9176b..8283963273506 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DiskBalancer.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DiskBalancer.java
@@ -892,7 +892,11 @@ private ExtendedBlock getBlockToCopy(FsVolumeSpi.BlockIterator iter,
       while (!iter.atEnd() && item.getErrorCount() < getMaxError(item)) {
         try {
           ExtendedBlock block = iter.nextBlock();
-
+          
+          //null pointer should not be passed to FsDatasetSpi.isValidBlock()
+          if(block == null){
+            return block;
+          }
           // A valid block is a finalized block, we iterate until we get
           // finalized blocks
           if (!this.dataset.isValidBlock(block)) {
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
index 208d554560d6e..1729c05960c8b 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/FsDatasetImpl.java
@@ -1816,7 +1816,10 @@ public List<ReplicaInfo> getFinalizedBlocks(String bpid) {
   @Override // FsDatasetSpi
   public void checkBlock(ExtendedBlock b, long minLength, ReplicaState state)
       throws ReplicaNotFoundException, UnexpectedReplicaStateException,
-      FileNotFoundException, EOFException, IOException {
+      FileNotFoundException, EOFException, IOException, NullPointerException {
+    if(b == null){
+      throw new NullPointerException("Input Block is null!");
+    }
     final ReplicaInfo replicaInfo = volumeMap.get(b.getBlockPoolId(), 
         b.getLocalBlock());
     if (replicaInfo == null) {