'Parse is_public into something usable.'

def _get_is_public(self, req):

    is_public = req.params.get('is_public')
    if (is_public is None):
        return True
    elif (is_public.lower() == 'none'):
        return None
    value = self._get_bool(is_public)
    if (value is None):
        raise exc.HTTPBadRequest(_('is_public    must    be    None,    True,    or    False'))
    return value
