DateTime(0.0) is not a None Value

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@14637 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Type/Accessor/TypeDefinition.py

@@ -103,7 +103,7 @@ type_definition = {
                              'isList'  : 0,
                            },
     'date'               : { 'cast'    : asDate,
-                             'null'    : ('', 'None', None, DateTime(0.0)),
+                             'null'    : ('', 'None', None,),
                              'default' : DateTime(0.0),
                              'isList'  : 0,
                            },