@Override
    public long count(final String childStreamType) throws IOException {
        final InternalSource childSource = getChild(childStreamType);
        Objects.requireNonNull(childSource, () ->
                LogUtil.message("No source found for childStreamType {}", childStreamType));

        return childSource.count();
    }
Creates a new file system stream source.

@return A new file system source.
stroom-data/stroom-data-store-impl-fs/src/main/java/stroom/data/store/impl/fs/FsSource.java