presto-spi/src/main/java/io/prestosql/spi/block/EncoderUtil.java/EncoderUtil/encodeNullsAsBits
class EncoderUtil:    @SuppressWarnings({"NarrowingCompoundAssignment", "ImplicitNumericConversion"})
    public static void encodeNullsAsBits(SliceOutput sliceOutput, Block block)
    {
        boolean mayHaveNull = block.mayHaveNull();
        sliceOutput.writeBoolean(mayHaveNull);
        if (!mayHaveNull) {
            return;
        }

        int positionCount = block.getPositionCount();
        for (int position = 0; position < (positionCount & ~0b111); position += 8) {
            byte value = 0;
            value |= block.isNull(position) ? 0b1000_0000 : 0;
            value |= block.isNull(position + 1) ? 0b0100_0000 : 0;
            value |= block.isNull(position + 2) ? 0b0010_0000 : 0;
            value |= block.isNull(position + 3) ? 0b0001_0000 : 0;
            value |= block.isNull(position + 4) ? 0b0000_1000 : 0;
            value |= block.isNull(position + 5) ? 0b0000_0100 : 0;
            value |= block.isNull(position + 6) ? 0b0000_0010 : 0;
            value |= block.isNull(position + 7) ? 0b0000_0001 : 0;
            sliceOutput.appendByte(value);
        }

        // write last null bits
        if ((positionCount & 0b111) > 0) {
            byte value = 0;
            int mask = 0b1000_0000;
            for (int position = positionCount & ~0b111; position < positionCount; position++) {
                value |= block.isNull(position) ? mask : 0;
                mask >>>= 1;
            }
            sliceOutput.appendByte(value);
        }
    }