code: public boolean addRequiredParams(JSType ...types) {
      if (hasOptionalOrVarArgs()) {
        return false;
      }
  
      for (JSType type : types) {
        newParameter(type);
      }
      return true;
    }
docs: Add parameters of the given type to the end of the param list.
  @return False if this is called after optional params are added.