presto-main/src/main/java/io/prestosql/operator/aggregation/multimapagg/MultimapAggregationStateSerializer.java/MultimapAggregationStateSerializer/MultimapAggregationStateSerializer
class MultimapAggregationStateSerializer:    public MultimapAggregationStateSerializer(Type keyType, Type valueType)
    {
        this.keyType = requireNonNull(keyType);
        this.valueType = requireNonNull(valueType);
        this.arrayType = new ArrayType(RowType.anonymous(ImmutableList.of(valueType, keyType)));
    }