docs: def parse_filter_params(query_params, filterable):
      """
      Parse query_params to a filter params dict. Merge multiple values for one key to a list.
      Filter out keys that aren't filterable.
  
      :param query_params: query params
      :param filterable: list of filterable keys
      :return: dict of filter values
      """
      if query_params is not None:
          filter_params = {}
          for fq in query_params.mixed():
              if fq in filterable:
                  filter_params[fq] = query_params.mixed().get(fq)
          return filter_params
      else:
          return {}