@Override
    public Fields getTermVectors(int docID) throws IOException {
        ensureOpen();
        return in
                .termVectors()
                .get(docID);
    }
This method is sugar for getting an {@link LeafReader} from
an {@link IndexReader} of any kind. If the reader is already atomic,
it is returned unchanged, otherwise wrapped by this class.
tika-eval/tika-eval-app/src/main/java/org/apache/tika/eval/app/tools/SlowCompositeReaderWrapper.java