private function addArgumentValues(AST\Expander $expander)
    {
        while (($argument = $this->getNextArgumentValue()) !== null) {
            $argument = ($argument === self::NULL_VALUE) ? null : $argument;
            $expander->addArgument($argument);
            if (!$this->lexer->isNextToken(Lexer::T_COMMA)) {
                break;
            }

            $this->lexer->moveNext();

            if ($this->lexer->isNextToken(Lexer::T_CLOSE_PARENTHESIS)) {
                $this->unexpectedSyntaxError($this->lexer->lookahead, 'string, number, boolean or null argument');
            }
        }
    }