Merge pull request z-song#5704 from asundust/patch-1

修正preg_match()函数第二个参数需要为字符串

Author: jxlwqq

src/Auth/Database/Administrator.php

@@ -47,7 +47,7 @@ public function __construct(array $attributes = [])
      */
     public function getAvatarAttribute($avatar)
     {
-        if (url()->isValidUrl($avatar)) {
+        if ($avatar && url()->isValidUrl($avatar)) {
             return $avatar;
         }