code: public T addSparkArg(String arg) {
      SparkSubmitOptionParser validator = new ArgumentValidator(false);
      validator.parse(Arrays.asList(arg));
      builder.userArgs.add(arg);
      return self();
    }
docs: Adds a no-value argument to the Spark invocation. If the argument is known, this method
  validates whether the argument is indeed a no-value argument, and throws an exception
  otherwise.
  <p>
  Use this method with caution. It is possible to create an invalid Spark command by passing
  unknown arguments to this method, since those are allowed for forward compatibility.
  
  @since 1.5.0
  @param arg Argument to add.
  @return This launcher.