docs: def QueryFields(r, what, fields=None):
      """
      Retrieves available fields for a resource.
  
      @type what: string
      @param what: Resource name, one of L{constants.QR_VIA_RAPI}
      @type fields: list of string
      @param fields: Requested fields
  
      @rtype: string
      @return: job id
      """
  
      query = {}
  
      if fields is not None:
          query["fields"] = ",".join(fields)
  
      return r.request("get", "/2/query/%s/fields" % what, query=query)