taiga webhook not work for tasks create, update, delete

[shagho]

Hi
I have an issue with taiga webhook.
I host the taiga in a vps and connect it to rocketchat.
In this connection CUD of all types like userstory, sprint and ... is worked except tasks.
This issue is like this issue.
I test somethings. when an task obj is passed in change or delete or create webhook in taiga/webhooks/tasks.py obj is Not None. but when obj is passed to serializer, serializer get is as None.