[FIX][IMP] account: set invoice_warn as non required

When reinitializing modules it is impossible to create partners if
account is installed because invoice_warn field has a required column
but no default value if the module does not depend from account. Use
case is trying to run test_mail tests with account installed.

As this field is not business critical it is now not required. As there
is a default value behavior should not change for users.

addons/account/models/account_invoice.py

@@ -662,7 +662,7 @@ class AccountInvoice(models.Model):
             # If partner has no warning, check its company
             if p.invoice_warn == 'no-message' and p.parent_id:
                 p = p.parent_id
-            if p.invoice_warn != 'no-message':
+            if p.invoice_warn and p.invoice_warn != 'no-message':
                 # Block if partner only has warning but parent company is blocked
                 if p.invoice_warn != 'block' and p.parent_id and p.parent_id.invoice_warn == 'block':
                     p = p.parent_id

addons/account/models/partner.py

@@ -414,7 +414,7 @@ class ResPartner(models.Model):
     contract_ids = fields.One2many('account.analytic.account', 'partner_id', string='Contracts', readonly=True)
     bank_account_count = fields.Integer(compute='_compute_bank_count', string="Bank")
     trust = fields.Selection([('good', 'Good Debtor'), ('normal', 'Normal Debtor'), ('bad', 'Bad Debtor')], string='Degree of trust you have in this debtor', default='normal', company_dependent=True)
-    invoice_warn = fields.Selection(WARNING_MESSAGE, 'Invoice', help=WARNING_HELP, required=True, default="no-message")
+    invoice_warn = fields.Selection(WARNING_MESSAGE, 'Invoice', help=WARNING_HELP, default="no-message")
     invoice_warn_msg = fields.Text('Message for Invoice')
 
     @api.multi

addons/account/views/partner_view.xml

@@ -151,7 +151,7 @@
                         <separator string="Warning on the Invoice" colspan="4"/>
                         <field name="invoice_warn" nolabel="1" />
                         <field name="invoice_warn_msg" colspan="3" nolabel="1"
-                                attrs="{'required':[('invoice_warn','!=','no-message')],'readonly':[('invoice_warn','=','no-message')]}"/>
+                                attrs="{'required':[('invoice_warn', '!=', False), ('invoice_warn','!=','no-message')],'readonly':[('invoice_warn','=','no-message')]}"/>
                     </group>
                 </page>
             </field>