HDFS-10496. DiskBalancer: ExecuteCommand checks planFile in a wrong way. Contributed by Lei (Eddy) Xu.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/diskbalancer/command/ExecuteCommand.java

@@ -61,7 +61,7 @@ public class ExecuteCommand extends Command {
     verifyCommandOptions(DiskBalancer.EXECUTE, cmd);
 
     String planFile = cmd.getOptionValue(DiskBalancer.EXECUTE);
-    Preconditions.checkArgument(planFile == null || planFile.isEmpty(),
+    Preconditions.checkArgument(planFile != null && !planFile.isEmpty(),
         "Invalid plan file specified.");
 
     String planData = null;