public function mutation($name, $class, $resolver = null)
    {
        $mutation = $this->mutations->findByName($name);

        if ($mutation) {
            return $mutation;
        }

        $operationScaffold = (new MutationScaffolder($name, null, $resolver, $class))
            ->setChainableParent($this);

        $this->mutations->push($operationScaffold);

        return $operationScaffold;
    }