presto-main/src/main/java/io/prestosql/operator/BigintGroupByHash.java/GetGroupIdsWork/GetGroupIdsWork
class GetGroupIdsWork:        public GetGroupIdsWork(Block block)
        {
            this.block = requireNonNull(block, "block is null");
            // we know the exact size required for the block
            this.blockBuilder = BIGINT.createFixedSizeBlockBuilder(block.getPositionCount());
        }