HDFS-10541. Diskbalancer: When no actions in plan, error message says "Plan was generated more than 24 hours ago". Contributed by Anu Engineer.

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

@@ -140,7 +140,7 @@ public class PlanCommand extends Command {
           .getBytes(StandardCharsets.UTF_8));
     }
 
-    if (plan != null) {
+    if (plan != null && plan.getVolumeSetPlans().size() > 0) {
       LOG.info("Writing plan to : {}", getOutputPath());
       try (FSDataOutputStream planStream = create(String.format(
           DiskBalancer.PLAN_TEMPLATE,