presto-main/src/main/java/io/prestosql/operator/BigintGroupByHash.java/BigintGroupByHash/appendValuesTo
class BigintGroupByHash:    @Override
    public void appendValuesTo(int groupId, PageBuilder pageBuilder, int outputChannelOffset)
    {
        checkArgument(groupId >= 0, "groupId is negative");
        BlockBuilder blockBuilder = pageBuilder.getBlockBuilder(outputChannelOffset);
        if (groupId == nullGroupId) {
            blockBuilder.appendNull();
        }
        else {
            BIGINT.writeLong(blockBuilder, valuesByGroupId.get(groupId));
        }

        if (outputRawHash) {
            BlockBuilder hashBlockBuilder = pageBuilder.getBlockBuilder(outputChannelOffset + 1);
            if (groupId == nullGroupId) {
                BIGINT.writeLong(hashBlockBuilder, NULL_HASH_CODE);
            }
            else {
                BIGINT.writeLong(hashBlockBuilder, BigintOperators.hashCode(valuesByGroupId.get(groupId)));
            }
        }
    }