add select

app/models/forms/CreatePostForm.php

@@ -10,7 +10,7 @@ class CreatePostForm extends FormModel
     {
         return [
             'content' => 'required|min-str-len:1',
-            'user_id' => 'required|min-str-len:1',
+            'user_id' => 'required',
         ];
     }
 }