Due to odoo/odoo#51075 it's an error to assign the `_date_name` field on
an empty recordset.
```
Traceback (most recent call last):
File "/home/odoo/src/odoo/14.0/odoo/models.py", line 1582, in _fields_view_get
arch_etree = getattr(self, '_get_default_%s_view' % view_type)()
File "/home/odoo/src/odoo/14.0/odoo/models.py", line 1495, in _get_default_calendar_view
self._date_name = dt
AttributeError: 'project.phase' object attribute '_date_name' is read-only
```
Issue observed on upgrade requests 2615 and 3121.
closesodoo/odoo#73401
X-original-commit: 1bbe88796a5b03ab1ab2faec1f0fe4f735fcb485
Signed-off-by: Christophe Simonis <chs@odoo.com>
Co-authored-by: Christophe Simonis <chs@odoo.com>