When syncing both Odoo and Outlook Calendar, if one Odoo event has an
attendee who does not have any email adress, it will lead to a traceback
error.
To reproduce the error:
1. Create a partner P who does not have an email address
2. In Calendar, create an event E with P
3. Sync with Outlook
Error: An Odoo Error is raised. When syncing from Outlook to Odoo, it
also sync the E-event (in case the latter has been updated on Outlook).
The Microsoft2Odoo syncing uses the email address of each attendee.
Since P does not have any, this creates the error.
Although Odoo allows the use of participants without email, this is not
the case for Outlook. On Outlook Calendar, as soon as a user adds an
attendee to an Event, Outlook will want to send an invitation before
saving this event (so, if the participant does not have any email
address, it won't be possible to save the event).
When syncing, the E-event will be added to Outlook Calendar. However,
for the same reasons as in the previous paragraph, it will not be
possible to update this event from Outlook Calendar.
Therefore, the solution is to prevent the user from having attendees
without email when his calendar is synchronized with Outlook.
OPW-2439027
closes odoo/odoo#67637
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>