src/Response.php
protected function handleResponseCallback($content, Closure $callback = null)
    {
        if ($callback instanceof Closure) {
            $content = call_user_func($callback, $content);
        }

        if (false === $content) {
            return $this->abort(404);
        } elseif (is_null($content)) {
            return new IlluminateResponse($content, 200);
        }

        return $content;
    }
protected function handleResponseCallback($content, Closure $callback = null)
    {
        if ($callback instanceof Closure) {
            $content = call_user_func($callback, $content);
        }

        if (false === $content) {
            return $this->abort(404);
        } elseif (is_null($content)) {
            return new IlluminateResponse($content, 200);
        }

        return $content;
    }
Handle response callback.

@param  mixed  $content
@param  \Closure|null  $callback

@return mixed