function _createNotFullyLoadedDirectory(directory) {
        if (!directory) {
            return Immutable.Map({
                notFullyLoaded: true,
                children: Immutable.Map()
            });
        }
        return directory.merge({
            notFullyLoaded: true,
            children: Immutable.Map()
        });
    }
@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