code: public static void addArgument(MethodCallExpr call, Expression arg) {
          List<Expression> args = call.getArgs();
          if (args == null) {
              args = new ArrayList<Expression>();
              call.setArgs(args);
          }
          args.add(arg);
      }
docs: Adds the given argument to the method call. The list of arguments will be
  initialized if it is <code>null</code>.
  
  @param call
  method call
  @param arg
  argument value