'Return a single group type item.'

@wsgi.Controller.api_version('3.11')
def show(self, req, id):

    context = req.environ['cinder.context']
    if ((id is not None) and (id == 'default')):
        grp_type = group_types.get_default_group_type()
        if (not grp_type):
            msg = _('Default    group    type    can    not    be    found.')
            raise exc.HTTPNotFound(explanation=msg)
        req.cache_resource(grp_type, name='group_types')
    else:
        try:
            grp_type = group_types.get_group_type(context, id)
            req.cache_resource(grp_type, name='group_types')
        except exception.GroupTypeNotFound as error:
            raise exc.HTTPNotFound(explanation=error.msg)
    return self._view_builder.show(req, grp_type)
