public function handle($old, $new)
    {
        if ( ! $this->canHandle($old) || ! $this->canHandle($new)) {
            return null;
        }

        if ($this->equals($old, $new)) {
            return false;
        }

        $this->lastException = new FailedConstraint(
            sprintf(
                '%s() body changed',
                $new->name
            )
        );

        return true;
    }