presto-main/src/main/java/io/prestosql/operator/PagesHash.java/PagesHash/isPositionNull
class PagesHash:    private boolean isPositionNull(int position)
    {
        long pageAddress = addresses.getLong(position);
        int blockIndex = decodeSliceIndex(pageAddress);
        int blockPosition = decodePosition(pageAddress);

        return pagesHashStrategy.isPositionNull(blockIndex, blockPosition);
    }