presto-spi/src/main/java/io/prestosql/spi/Page.java/Page/getSingleValuePage
class Page:    public Page getSingleValuePage(int position)
    {
        Block[] singleValueBlocks = new Block[this.blocks.length];
        for (int i = 0; i < this.blocks.length; i++) {
            singleValueBlocks[i] = this.blocks[i].getSingleValueBlock(position);
        }
        return new Page(1, singleValueBlocks);
    }