HBASE-13901 Error while calling watcher on creating and deleting an HBase table

Signed-off-by: Andrew Purtell <apurtell@apache.org>

hbase-client/src/main/java/org/apache/hadoop/hbase/zookeeper/ZKUtil.java

@@ -660,7 +660,7 @@ public class ZKUtil {
       return node;
     }
     public boolean isEmpty() {
-      return (data.length == 0);
+      return (data == null || data.length == 0);
     }
   }