function _getCondensedForm(filter) {
        if (!_.isArray(filter)) {
            return "";
        }

        // Format filter in condensed form
        if (filter.length > 2) {
            return filter.slice(0, 2).join(", ") + " " +
                   StringUtils.format(Strings.FILE_FILTER_CLIPPED_SUFFIX, filter.length - 2);
        }
        return filter.join(", ");
    }
Get the condensed form of the filter set by joining the first two in the set with
a comma separator and appending a short message with the number of filters being clipped.
@param {Array.<string>} filter
@return {string} Condensed form of filter set if `filter` is a valid array.
                 Otherwise, return an empty string.