Simplification: set default to 0 if not set, which removes the need for Dummy class instance, and factorises 2 branches of a test.
Micro optimisation: fetch the persistent mapping only from self only once (prevents instanciating 2 acquisition wrappers out of 3).
Improve coding style (space around operators).


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@29083 20353a03-c40f-0410-a6d1-a30d3c3de9de