Mass mailing has a wizard to import contacts from a text input. It currently
crashes when trying to import a void field, while it should not.
We fix that by two means
* make field required in view (as model cannot be modified);
* while it is not updated, simply consider a void input should not crash and
is considered as an input without valid input found;
Task-3053031
closesodoo/odoo#104769
X-original-commit: aa183fa29d609d2b608fa451ee48a35e3d1549b2
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>