I'm triying to achieve a custom filter for partner

here is the domain filter on menu partner

['|',('activity_ids', '=', False), ('activity_ids.date_deadline', '<=', context_today().strftime('%Y-%m-%d'))]

So we want partner with no activities at all or with late activities. But it only gives partner with late activities, the first constraint seems to be ignored.

I tried the first one alone and it is working, partner with no activities are displayed but when I add the or operator and the second part it returns only results of the second part (with late actvities)...