[IMP] mail.mail: simplify: no default for headers field

This avoids storing useless "{}" values
in the database when there are no headers,
and avoids having to update all existing
entries when this column is added.
Just requires simple tests before evaluating
the headers contents.

addons/mail/mail_group.py

@@ -221,10 +221,12 @@ def get_suggested_thread(self, cr, uid, removed_suggested_threads=None, context=
     def message_get_email_values(self, cr, uid, id, notif_mail=None, context=None):
         res = super(mail_group, self).message_get_email_values(cr, uid, id, notif_mail=notif_mail, context=context)
         group = self.browse(cr, uid, id, context=context)
-        try:
-            headers = eval(res.get('headers', '{}'))
-        except Exception:
-            headers = {}
+        headers = {}
+        if res.get('headers'):
+            try:
+                headers.update(eval(res['headers']))
+            except Exception:
+                pass
         headers['Precedence'] = 'list'
         # avoid out-of-office replies from MS Exchange
         # http://blogs.technet.com/b/exchange/archive/2006/10/06/3395024.aspx
@@ -236,5 +238,5 @@ def message_get_email_values(self, cr, uid, id, notif_mail=None, context=None):
             # X-Forge-To: will replace To: after SMTP envelope is determined by ir.mail.server
             list_to = '"%s" <%s@%s>' % (group.name, group.alias_name, group.alias_domain)
             headers['X-Forge-To'] = list_to
-        res['headers'] = '%s' % headers
+        res['headers'] = repr(headers)
         return res

addons/mail/mail_mail.py

@@ -67,7 +67,6 @@ class mail_mail(osv.Model):
 
     _defaults = {
         'state': 'outgoing',
-        'headers': '{}',
     }
 
     def default_get(self, cr, uid, fields, context=None):

addons/website_mail_group/models/mail_group.py

@@ -13,16 +13,18 @@ def message_get_email_values(self, cr, uid, id, notif_mail=None, context=None):
         res = super(MailGroup, self).message_get_email_values(cr, uid, id, notif_mail=notif_mail, context=context)
         group = self.browse(cr, uid, id, context=context)
         base_url = self.pool['ir.config_parameter'].get_param(cr, uid, 'web.base.url')
-        try:
-            headers = eval(res.get('headers', '{}'))
-        except Exception:
-            headers = {}
+        headers = {}
+        if res.get('headers'):
+            try:
+                headers = eval(res['headers'])
+            except Exception:
+                pass
         headers.update({
             'List-Archive': '<%s/groups/%s>' % (base_url, slug(group)),
             'List-Subscribe': '<%s/groups>' % (base_url),
             'List-Unsubscribe': '<%s/groups?unsubscribe>' % (base_url,),
         })
-        res['headers'] = '%s' % headers
+        res['headers'] = repr(headers)
         return res