code: function (model, filter, value) {
  
      if (!_.isString(filter)) {
          return null;
      }
  
      if (model.data) {
          var list = findKeys(model.data, filter)
              , values = [];
  
          for (var res in list) {
  
              if (value === undefined || list[res][filter] === value) {
                  values.push(res);
              }
          }
      }
      //return _.isEmpty(values) ? undefined : values;
      //Changed to return empty array instead of 'undefined'. Do not change back, otherwise some functions working with arrays do not work properly.
      return values;
  }
docs: Finds all nodes with filter property in given model and returns array list of nodes
  @param model
  @param filter
  @returns {*}