presto-spi/src/main/java/io/prestosql/spi/block/AbstractRowBlock.java/AbstractRowBlock/isNull
class AbstractRowBlock:    @Override
    public boolean isNull(int position)
    {
        checkReadablePosition(position);
        boolean[] rowIsNull = getRowIsNull();
        return rowIsNull != null && rowIsNull[position + getOffsetBase()];
    }