Clarify the case of list/set accessors when no value is defined: they return None.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@17861 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Type/Accessor/List.py

@@ -310,7 +310,8 @@ class SetGetter(ListGetter):
 
     def __call__(self, instance, *args, **kw):
       result_list = ListGetter.__call__(self, instance, *args, **kw)
-      result_set = dict([(x, 0) for x in result_list]).keys()
-      return result_set
+      if result_list is not None:
+        result_set = dict([(x, 0) for x in result_list]).keys()
+        return result_set
 
 Tester = Base.Tester

product/ERP5Type/tests/testERP5Type.py

@@ -1699,16 +1699,18 @@ class TestPropertySheet:
       self.assertTrue(hasattr(person, 'getDummyList'))
 
       self.assertEquals(person.getDummy(), None)
-      # self.assertEquals(person.getDummyList(), []) # XXX what is the default
-                                                     # value for a list getter ?
+      self.assertEquals(person.getDummyList(), None)
+      self.assertEquals(person.getDummySet(), None)
 
       person.setDummyList(['a', 'b'])
       self.assertEquals(person.getDummy(), 'a')
       self.assertEquals(person.getDummyList(), ['a', 'b'])
+      self.assertEquals(person.getDummySet(), ['a', 'b'])
 
       person.setDummy('value')
       self.assertEquals(person.getDummy(), 'value')
       self.assertEquals(person.getDummyList(), ['value'])
+      self.assertEquals(person.getDummySet(), ['value'])