Use exception handlers instead of JsonApiSerializableInterface

src/Api/Handler/ModelNotFoundExceptionHandler.php

@@ -0,0 +1,38 @@
+<?php
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Api\Handler;
+
+use Exception;
+use Illuminate\Database\Eloquent\ModelNotFoundException;
+use Tobscure\JsonApi\Exception\Handler\ExceptionHandlerInterface;
+use Tobscure\JsonApi\Exception\Handler\ResponseBag;
+
+class ModelNotFoundExceptionHandler implements ExceptionHandlerInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function manages(Exception $e)
+    {
+        return $e instanceof ModelNotFoundException;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function handle(Exception $e)
+    {
+        $status = 404;
+        $error = [];
+
+        return new ResponseBag($status, [$error]);
+    }
+}