public static <T_ROW> ColumnBuilder<T_ROW, String, TextCell> iecByteStringColumnBuilder(
            final Function<T_ROW, Long> bytesExtractor, final String valueIfNull) {

        final Function<T_ROW, String> bytesAsStrExtractor = row -> {
            if (row == null || bytesExtractor == null) {
                return valueIfNull;
            } else {
                final Long bytes = bytesExtractor.apply(row);
                if (bytes == null) {
                    return valueIfNull;
                } else {
                    return ModelStringUtil.formatIECByteSizeString(bytes);
                }
            }
        };

        return new ColumnBuilder<T_ROW, String, TextCell>(bytesAsStrExtractor, TextCell::new);
    }
A simple text cell with the value of the hover tooltip provided by tooltipFunction, which is
applied to the cell value.
stroom-core-client/src/main/java/stroom/util/client/DataGridUtil.java