Since db922a6a, it could happen that the
aggregated `dest_ids` array from `read_group()` in
`account.fiscal.position.map_tax()` contained `None` elements. These
None elements are added to `result_ids` by the current set
comprehension. In that case an exception is raised from
https://github.com/odoo/odoo/blob/1305e87a3873970ee5c0aa21bc749ba33375e517/odoo/models.py#L6176


after passing `result_ids` to `browse()`.

opw-3742597
opw-3742305
opw-3742596
opw-3742217

closes odoo/odoo#153879

Signed-off-by: de Wouters de Bouchout Jean-Benoît (jbw) <jbw@odoo.com>
Co-authored-by: Alvaro Fuentes <afu@odoo.com>