private function normalizeValue(string $value, string $operator)
    {
        if (!is_numeric($value)) {
            $this->getLogger()->notice('Invalid filter ignored', [
                'exception' => new InvalidArgumentException(sprintf('Invalid value for "[%s]", expected number', $operator)),
            ]);

            return null;
        }

        return $value + 0; // coerce $value to the right type.
    }