src/Parameter/Parser/ValueParser.php
public function parse($inputString): ?string
    {
        $output = parent::parse($this->getNonAttributePart($inputString));

        if ($this->getCurrentState() == self::STATE_IN_NON_QUOTED_VALUE) {
            return $output;
        }

        if ($output == '') {
            return null;
        }

        $quotedStringParser = new QuotedStringParser();
        $quotedString = $quotedStringParser->parse($output);

        return $quotedString->getValue();
    }
public function parse($inputString): ?string
    {
        $output = parent::parse($this->getNonAttributePart($inputString));

        if ($this->getCurrentState() == self::STATE_IN_NON_QUOTED_VALUE) {
            return $output;
        }

        if ($output == '') {
            return null;
        }

        $quotedStringParser = new QuotedStringParser();
        $quotedString = $quotedStringParser->parse($output);

        return $quotedString->getValue();
    }
@param string $inputString

@return string