Cannot delete attachment `"attachment in body: None is not of type 'object'"`

```
curl -X DELETE "$SERVER/buckets/$BID/collections/$CID/records/$RID/attachment" -H "Authorization: $AUTH"

{"code":400,"errno":107,"error":"Invalid parameters","message":"attachment in body: None is not of type 'object'","details":[{"location":"body","name":"attachment","description":"None is not of type 'object'"}]}%
```

