FIX

partner_firstname/res_user.py

@@ -42,8 +42,7 @@ class ResUsers(orm.Model):
             res_partner = self.pool.get('res.partner')
             partner = res_partner.browse(cr, user, vals2['partner_id'],
                                          context)
-            if partner.lastname:
-                vals2['lastname'] = partner.lastname
+            vals2['lastname'] = partner.lastname
         elif 'login' in vals and 'lastname' not in vals:
             vals2['lastname'] = vals2['login']
         return super(ResUsers, self).create(cr, user, vals2, context=context)