Check whether file exists and give a more descriptive message

src/Exceptions/FileNotFoundException.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace Mpociot\ApiDoc\Exceptions;
+
+use Symfony\Component\HttpKernel\Exception\HttpException;
+
+class FileNotFoundException extends HttpException
+{
+    public function __construct(int $statusCode, string $message = null, Throwable $previous = null, array $headers = [], ?int $code = 0)
+    {
+        parent::__construct($statusCode, $message);
+    }
+}

src/Http/Controller.php

@@ -3,6 +3,7 @@
 namespace Mpociot\ApiDoc\Http;
 
 use Illuminate\Support\Facades\Storage;
+use Mpociot\ApiDoc\Exceptions\FileNotFoundException;
 
 class Controller
 {
@@ -18,6 +19,10 @@ public function html()
      */
     public function json()
     {
+        if (!Storage::disk(config('apidoc.storage'))->has('apidoc/collection.json')) {
+            throw new FileNotFoundException(400, 'Please run php artisan apidoc:generate.');
+        }
+
         return response()->json(
             json_decode(Storage::disk(config('apidoc.storage'))->get('apidoc/collection.json'))
         );