private FsSource child(final String streamTypeName) {
        final Path childFile = fileSystemStreamPathHelper.getChildPath(getFile(), streamTypeName);
        boolean lazy = fileSystemStreamPathHelper.isStreamTypeLazy(streamTypeName);
        boolean isFile = Files.isRegularFile(childFile);
        if (lazy || isFile) {
            return new FsSource(fileSystemStreamPathHelper, this, streamTypeName, childFile);
        } else {
            return null;
        }
    }
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