    private function filterScheme($scheme)
    {
        if (!is_string($scheme)) {
            throw new \InvalidArgumentException('Scheme must be a string');
        }

        return strtolower($scheme);
    }
The software constructs all or part of an SQL command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended SQL command when it is sent to a downstream component.