HDFS-12406. dfsadmin command prints "Exception encountered" even if there is no exception, when debug is enabled. Contributed by Nandakumar.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DFSAdmin.java

@@ -2244,7 +2244,7 @@ public class DFSAdmin extends FsShell {
       System.err.println(cmd.substring(1) + ": "
                          + e.getLocalizedMessage());
     }
-    if (LOG.isDebugEnabled()) {
+    if (LOG.isDebugEnabled() && debugException != null) {
       LOG.debug("Exception encountered:", debugException);
     }
     return exitCode;