A quick hack instead of jerome's patch. Hope it is enough.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@16347 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/File.py

@@ -84,6 +84,7 @@ class File(Document, CMFFile, ConversionCacheMixin):
 
   # Default global values
   content_type = '' # Required for WebDAV support (default value)
+  data = 'Empty File' # A hack required to use OFS.Image.index_html without calling OFS.Image.__init__
 
   # Default Properties
   property_sheets = ( PropertySheet.Base