protected function matchToKeys(array $matches)
    {
        $parameterNames = $this->parameterNames();

        if (count($parameterNames) == 0) {
            return array();
        }

        $parameters = array_intersect_key($matches, array_flip($parameterNames));

        return array_filter($parameters, function ($value)
        {
            return is_string($value) && (strlen($value) > 0);
        });
    }