presto-main/src/main/java/io/prestosql/operator/aggregation/KeyValuePairs.java/KeyValuePairs/deserialize
class KeyValuePairs:    private void deserialize(Block block)
    {
        for (int i = 0; i < block.getPositionCount(); i += 2) {
            add(block, block, i, i + 1);
        }
    }