[FIX][IMP] purchase: set purchase_warn as non required

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

See also 71181a0e39, dd47abdcc3 and 06a02ae4c2.

addons/purchase/models/purchase.py

@@ -261,7 +261,7 @@ class PurchaseOrder(models.Model):
         if partner.purchase_warn == 'no-message' and partner.parent_id:
             partner = partner.parent_id
 
-        if partner.purchase_warn != 'no-message':
+        if partner.purchase_warn and partner.purchase_warn != 'no-message':
             # Block if partner only has warning but parent company is blocked
             if partner.purchase_warn != 'block' and partner.parent_id and partner.parent_id.purchase_warn == 'block':
                 partner = partner.parent_id

addons/purchase/models/res_partner.py

@@ -26,5 +26,5 @@ class res_partner(models.Model):
         help="This currency will be used, instead of the default one, for purchases from the current partner")
     purchase_order_count = fields.Integer(compute='_purchase_invoice_count', string='Purchase Order Count')
     supplier_invoice_count = fields.Integer(compute='_purchase_invoice_count', string='# Vendor Bills')
-    purchase_warn = fields.Selection(WARNING_MESSAGE, 'Purchase Order', help=WARNING_HELP, required=True, default="no-message")
+    purchase_warn = fields.Selection(WARNING_MESSAGE, 'Purchase Order', help=WARNING_HELP, default="no-message")
     purchase_warn_msg = fields.Text('Message for Purchase Order')

addons/purchase/views/res_partner_views.xml

@@ -84,7 +84,7 @@
                         <separator string="Warning on the Purchase Order" colspan="4"/>
                         <field name="purchase_warn" nolabel="1" />
                         <field name="purchase_warn_msg" colspan="3" nolabel="1" 
-                                attrs="{'required':[('purchase_warn','!=','no-message')],'readonly':[('purchase_warn','=','no-message')]}"/>
+                                attrs="{'required':[('purchase_warn', '!=', False), ('purchase_warn','!=','no-message')],'readonly':[('purchase_warn','=','no-message')]}"/>
                     </group>
                 </page>
             </field>