presto-orc/src/main/java/io/prestosql/orc/LazySliceInput.java/LazySliceInput/getDelegate
class LazySliceInput:    private SliceInput getDelegate()
    {
        if (delegate == null) {
            delegate = requireNonNull(loader.get(), "loader returned a null stream");
            verify(delegate.length() == globalLength, "loader returned stream of length %s, but length %s was expected", delegate.length(), globalLength);
            delegate.setPosition(initialPosition);
        }
        return delegate;
    }