with our slightly modified Odoo (V12), we are trying to fetch Data via external API from odoo.

while fetching res.partner we get following Error:

TypeError: cannot marshal <class 'datetime.date'> objects

the fetched Object has the following datetime/date values

'write_date': datetime.datetime(2018, 10, 16, 11, 56, 51, 417000),
'uid_nr_check': datetime.date(2018, 10, 1),
'__last_update': datetime.datetime(2018, 10, 16, 11, 56, 51, 417000),

uid_nr_check is defined as:

 uid_nr_check = fields.Date(string="last UID Number check")

any ideas whats wrong? we use nighly build of odoo 12 on debian.