code: function _createNotFullyLoadedDirectory(directory) {
          if (!directory) {
              return Immutable.Map({
                  notFullyLoaded: true,
                  children: Immutable.Map()
              });
          }
          return directory.merge({
              notFullyLoaded: true,
              children: Immutable.Map()
          });
      }
docs: @private
  
  Creates a directory object (or updates an existing directory object) to look like one
  that has not yet been loaded, but in which we want to start displaying entries.
  @param {Immutable.Map=} directory Directory entry to update
  @return {Immutable.Map} New or updated directory object