HDFS-13261. Fix incorrect null value check. Contributed by Jianfei Jiang.

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocol/ZoneReencryptionStatus.java

@@ -223,7 +223,7 @@ public class ZoneReencryptionStatus {
    * a listReencryptionStatus call, for the crypto admin to consume.
    */
   public void setZoneName(final String name) {
-    Preconditions.checkNotNull(name == null);
+    Preconditions.checkNotNull(name, "zone name cannot be null");
     zoneName = name;
   }
 

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

@@ -145,7 +145,7 @@ public class AdminHelper {
     private final Command[] commands;
 
     public HelpCommand(Command[] commands) {
-      Preconditions.checkNotNull(commands != null);
+      Preconditions.checkNotNull(commands, "commands cannot be null.");
       this.commands = commands;
     }