code: def path(self, which=None):
          
          if which == 'refresh':
              return '{0}/{1}'.format(
                  super(ExternalUserGroup, self).path(which='self'),
                  which
              )
          return super(ExternalUserGroup, self).path(which)
docs: Extend ``nailgun.entity_mixins.Entity.path``.
  
          The format of the returned path depends on the value of ``which``:
  
          refresh
              /api/usergroups/:usergroup_id/external_usergroups/:id/refresh