Make sure user_group_id is rendered as int where relevant.

app/Models/TransactionGroup.php

@@ -46,6 +46,8 @@ class TransactionGroup extends Model
             'deleted_at' => 'datetime',
             'title'      => 'string',
             'date'       => 'datetime',
+            'user_id'                => 'integer',
+            'user_group_id'                => 'integer',
         ];
 
     protected $fillable = ['user_id', 'user_group_id', 'title'];