Logical error on printing/re-printing invoice

OpenERP-Server Version : 5.0.1
Normaly if you reprinting an invoice when you have already printed one time, OpenERP resend to you the first version of invoice (if you have let the 'attachment_use' field filled).
This functionnality works only in you have put an invoice description. If you doesn't filled the description field, OpenERP recreate the requested invoice on the fly.
I propose to modify 'document.py' file like bellow:
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diff --git a/addons/document/document.py b/addons/document/document.py
index 1a66145..dd36fd7 100644
--- a/addons/document/document.py
+++ b/addons/document/document.py
@@ -667,7 +667,8 @@ class document_file(osv.osv):
             result = obj_model.read(cr, uid, [vals['res_id']], context=context)
             if len(result):
                 obj=result[0]
- vals['title'] = (obj.get('name',''))[:60]
+ if obj.get('name',''): #[HNM] without this test If 'Description' field of invoice object isn't filled you cannot create attachment.
+ vals['title'] = (obj.get('name',''))[:60]
                 if obj_model._name=='res.partner':
                     vals['partner_id']=obj['id']
                 elif obj.get('address_id',False):
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Regards