Suppose that a Task is added on a task via a studio customisation.
Then the _get_message_needaction method gets called on the onchange of the
toplevel task, which triggers another call to _get_message_needaction.
During that update, we get a self with a model.newID; its ids field is empty,
so the list of tasks res itself is empty.
As a result the method crashes on a malformed query.
This can in turn prevent the completion of some higher-level operation,
e.g. a state change on the task.
opw 1909043
closesodoo/odoo#29084
len-odoo
d1490e2777