[FIX] missing subject in fetched mail causes exception

fetchmail_attach_from_folder/__openerp__.py

@@ -22,7 +22,7 @@
 
 {
     'name': 'Attach mails in an IMAP folder to existing objects',
-    'version': '1.0',
+    'version': '1.0.1',
     'description': """
     Adds the possibility to attach emails from a certain IMAP folder to objects,
     ie partners. Matching is done via several algorithms, ie email address.

fetchmail_attach_from_folder/model/fetchmail_server.py

@@ -209,7 +209,7 @@ class fetchmail_server(Model):
                             'res_id': object_id,
                             'body_text': mail_message.get('body'),
                             'body_html': mail_message.get('body_html'),
-                            'subject': mail_message.get('subject'),
+                            'subject': mail_message.get('subject') or '',
                             'email_to': mail_message.get('to'),
                             'email_from': mail_message.get('from'),
                             'email_cc': mail_message.get('cc'),