public static void addDef(List<String> args, String name, String val) {
    if (val != null) {
      args.add("-D");
      args.add(name + "=" + val);
    }
  }
Add a Hadoop command line definition to args if the value is
not null.
hcatalog/webhcat/svr/src/main/java/org/apache/hive/hcatalog/templeton/LauncherDelegator.java