Hard coded allow_none=True

was getting error "TypeError: cannot marshal None unless allow_none is enabled"

referred to comment by Naresh Soni to this answer: http://help.openerp.com/question/14108/typeerror-cannot-marshal-none-unless-allow_none-is-enabled/?answer=14136#post-id-14136

This serves my purpose, so I am not going to make this configurable.