set the default value of title as the empty string

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@11162 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Type/PropertySheet/DublinCore.py

@@ -39,6 +39,7 @@ class DublinCore:
             'type'        : 'string',
             'translatable'  : 1,
             'translation_domain' : 'erp5_content',
+            'default'     : '',
             'mode'        : 'w' },
         {   'id'          : 'subject',
             'description' : '',