@Override
        public DataRange getDataRange() {
            return Optional.ofNullable(lastResult)
                    .map(AbstractFetchDataResult::getSourceLocation)
                    .flatMap(SourceLocation::getOptDataRange)
                    .orElse(DataRange.fromByteOffset(0));
        }
Used for navigating HexDump data which has to navigate using byte offsets,
not char offsets.
stroom-core-client/src/main/java/stroom/data/client/presenter/SourcePresenter.java