code: private Node createParameters(boolean lastVarArgs, JSType... parameterTypes) {
      FunctionParamBuilder builder = new FunctionParamBuilder(this);
      int max = parameterTypes.length - 1;
      for (int i = 0; i <= max; i++) {
        if (lastVarArgs && i == max) {
          builder.addVarArgs(parameterTypes[i]);
        } else {
          builder.addRequiredParams(parameterTypes[i]);
        }
      }
      return builder.build();
    }
docs: Creates a tree hierarchy representing a typed argument list.
  
  @param lastVarArgs whether the last type should considered as a variable length argument.
  @param parameterTypes the parameter types. The last element of this array is considered a
  variable length argument is {@code lastVarArgs} is {@code true}.
  @return a tree hierarchy representing a typed argument list