public function resolveTransformer()
    {
        if (is_string($this->resolver)) {
            return $this->container->make($this->resolver);
        } elseif (is_callable($this->resolver)) {
            return call_user_func($this->resolver, $this->container);
        } elseif (is_object($this->resolver)) {
            return $this->resolver;
        }

        throw new RuntimeException('Unable to resolve transformer binding.');
    }