src/Console/EventListener/XdebugListener.php
protected function getIdeKeyFromInputOption(InputInterface $input): ?string
    {
        $optionValue = $input->getOption(self::OPTION_XDEBUG);

        if ($optionValue === null) { // no custom value was passed => use default
            return self::DEFAULT_VALUE;
        }

        if ($optionValue === '') { // empty value was passed => do not enable the feature
            return null;
        }

        return $optionValue;
    }
protected function getIdeKeyFromInputOption(InputInterface $input): ?string
    {
        $optionValue = $input->getOption(self::OPTION_XDEBUG);

        if ($optionValue === null) { // no custom value was passed => use default
            return self::DEFAULT_VALUE;
        }

        if ($optionValue === '') { // empty value was passed => do not enable the feature
            return null;
        }

        return $optionValue;
    }
If --xdebug option was not passed at all, return null to not activate the feature.
If the option was used without a value, use the default value of idekey.
If the option was passed with custom (not empty) value, use this value.