How to use the react-admin.fetchUtils.flattenObject function in react-admin

const composeFilter = (paramsFilter) => {
    const flatFilter = fetchUtils.flattenObject(paramsFilter)
    const filter = Object.keys(flatFilter).map(key => {
      const splitKey = key.split('||');
      let ops = splitKey[1] ? splitKey[1] : 'cont';
      let field = splitKey[0];
      // code below allows multifield filters in react admin (date range for example). Here is an example:
      //
      // 
      //   
      //   
      // 
      if (field.indexOf('_') == 0 && field.indexOf('.') > -1) {
        field = field.split(/\.(.+)/)[1];
      }
      return field + '||' + ops + '||' + flatFilter[key];
    })
    return filter;

const composeFilter = (paramsFilter) => {

    if (paramsFilter === '' || (typeof paramsFilter.q !== 'undefined' && paramsFilter.q === '')) {
      paramsFilter = {}
    }

    const flatFilter = fetchUtils.flattenObject(paramsFilter);
    const filter = Object.keys(flatFilter).map(key => {
      const splitKey = key.split('||');
      const ops = splitKey[1] ? splitKey[1] : 'cont';
      let field = splitKey[0];

      if (field.indexOf('_') === 0 && field.indexOf('.') > -1) {
        field = field.split(/\.(.+)/)[1];
      }
      return { field, operator: ops, value: flatFilter[key] };
    });
    return filter;
  };

query[params.target] = params.id
        }
      case GET_LIST:
        const {page, perPage} = params.pagination || {}
        const {field, order} = params.sort || {}
        const sortKey = `$sort[${field === 'id' ? idKey : field}]`
        dbg('field=%o, sort-key=%o', field, sortKey)
        let sortVal = order === 'DESC' ? -1 : 1
        if (perPage && page) {
          query['$limit'] = perPage
          query['$skip'] = perPage * (page - 1)
        }
        if (order) {
          query[sortKey] = JSON.stringify(sortVal)
        }
        Object.assign(query, fetchUtils.flattenObject(params.filter));
        dbg('query=%o', query)
        return service.find({query})
      case GET_ONE:
        return service.get(params.id)
      case UPDATE:
        if (usePatch) {
          const data = params.previousData ? diff(params.previousData, params.data) : params.data
          return service.patch(params.id, data)
        }
        return service.update(params.id, params.data)
      case CREATE:
        return service.create(params.data)
      case DELETE:
        return service.remove(params.id)
      default:
        throw new Error(`Unsupported FeathersJS restClient action type ${type}`)

const convertDataRequestToHTTP = (apiUrl, type, resource, params) => {
  let url = "";
  const options = {
    headers: new Headers({
      Accept: "application/json"
    })
  };
  switch (type) {
    case GET_LIST: {
      const { page, perPage } = params.pagination;
      const { field, order } = params.sort;
      let _field = field === "id" ? "_id" : field;
      const query = {
        ...fetchUtils.flattenObject(params.filter),
        sort: order === "DESC" ? `-${_field}` : _field,
        page: page,
        limit: perPage
      };
      url = `${apiUrl}/${resource}?${stringify(query)}`;
      break;
    }
    case GET_ONE:
      url = `${apiUrl}/${resource}/${params.id}`;
      break;
    case CREATE:
      url = `${apiUrl}/${resource}`;
      options.method = "POST";
      options.body = JSON.stringify(params.data);
      break;
    case UPDATE:

_sort: field,
                    _order: order,
                    _start: (page - 1) * perPage,
                    _end: page * perPage,
                };
                url = `${apiUrl}/${resource}?${stringify(query)}`;
                break;
            }
            case GET_ONE:
                url = `${apiUrl}/${resource}/${params.id}`;
                break;
            case GET_MANY_REFERENCE: {
                const { page, perPage } = params.pagination;
                const { field, order } = params.sort;
                const query = {
                    ...fetchUtils.flattenObject(params.filter),
                    [params.target]: params.id,
                    _sort: field,
                    _order: order,
                    _start: (page - 1) * perPage,
                    _end: page * perPage,
                };
                url = `${apiUrl}/${resource}?${stringify(query)}`;
                break;
            }
            case UPDATE:
                url = `${apiUrl}/${resource}/${params.id}`;
                options.method = 'PUT';
                options.body = JSON.stringify(params.data);
                break;
            case CREATE:
                url = `${apiUrl}/${resource}`;