docs: def init(req, model):  # pylint: disable=unused-argument
      """ Determine the sparse fields to limit the response to
  
      Return a dict where the key is the resource type (rtype) &
      the value is an array of string fields names to whitelist
      against.
  
      :return:
          dict
      """
  
      params = {}
  
      for key, val in req.params.items():
          try:
              rtype, fields = _parse_param(key, val)
              params[rtype] = fields
          except TypeError:
              continue
  
      if params:
          _validate_req(req)
          for rtype, fields in params.items():
              _validate_param(rtype, fields)
      return params