[web2py] custom validator _and in IS_IN_DB doesn't get called

[dustin.b]

hi my secound stupid beginner question but i cant get behind it.

i have a list:ref.. to choose multiple values but i need it to be not
empty. the problem when i use the IS_NOT_EMPTY validator is that the
field is not empty but "||" for an empty list i think (thats what i
have in database in this case)

so i started to write my own Validator and check against that. this
isnt my first validator , but this time i doesn't work as i exspect.
every time i submit the form only "INIT IS_NOT_EMPTY_LIST" is printet
out .. but no "CALL IS_NOT_EMPTY_LIST" .. as in my other validators.

if there is an other way around checking empty lists this would be
also fine ..

here's the code

class IS_NOT_EMPTY_LIST(object):
    def __init__(self, unused, error_message='failed ..'):
        self.unused = unused
        self.error_message = error_message
        print "INIT IS_NOT_EMPTY_LIST"
    def __call__(self, value):
        print "CALL IS_NOT_EMPTY_LIST"
        try:
            if value == "||" and value == "":
                return (value, self.error_message)
            else:
                return (value, None)
        except:
            return (value, self.error_message)

db.define_table('element', Field('name'))

db.define_table('data', Field('name', 'string'),
Field('elements','list:reference element' ))

db.data.elements.requires = IS_IN_DB(db,'element.id',multiple=True,
_and=IS_NOT_EMPTY_LIST(None, error_message='foo'))