presto-main/src/main/java/io/prestosql/operator/aggregation/multimapagg/MultimapAggregationFunction.java/MultimapAggregationFunction/input
class MultimapAggregationFunction:    public static void input(MultimapAggregationState state, Block key, Block value, int position)
    {
        state.add(key, value, position);
    }