HDFS-6285. tidy an error log inside BlockReceiver. Contributed by Liang Xie.

(cherry picked from commit 7b1ea9c481)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -366,6 +366,8 @@ Release 2.8.0 - UNRELEASED
     HDFS-3384. DataStreamer thread should be closed immediatly when failed to
     setup a PipelineForAppendOrRecovery (Uma Maheswara Rao G via vinayakumarb)
 
+    HDFS-6285. tidy an error log inside BlockReceiver. (Liang Xie via umamahesh)
+
 Release 2.7.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockReceiver.java

@@ -262,8 +262,8 @@ class BlockReceiver implements Closeable {
       
       // check if there is a disk error
       IOException cause = DatanodeUtil.getCauseIfDiskError(ioe);
-      DataNode.LOG.warn("IOException in BlockReceiver constructor. Cause is ",
-          cause);
+      DataNode.LOG.warn("IOException in BlockReceiver constructor"
+          + (cause == null ? "" : ". Cause is "), cause);
       
       if (cause != null) { // possible disk error
         ioe = cause;