json2pb::ProtoMessageToJson 将pb转为json,当遇到oneof时出错

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如下代码，使用json2pb将pb转为json,当遇到oneof时输出json与protobuf不一致

#include <json2pb/pb_to_json.h>
#include <google/protobuf/util/json_util.h>
#include "test.pb.h"
/*
 * test.proto
 *
syntax = "proto3";

message Test{
    oneof OneOf{
        string a = 1;
        string b = 2;
        string c = 3;
    }
}
 */
int main()
{
    Test test;
    test.set_a("aaa");
    {
        std::string strJson;
        json2pb::Pb2JsonOptions options;
        options.always_print_primitive_fields = true;

        json2pb::ProtoMessageToJson(test, &strJson, options);
        std::cout << "json2pb: " << strJson << std::endl;
    }
    {
        std::string strJson;
        google::protobuf::util::JsonOptions options;
        options.always_print_primitive_fields = true;

        google::protobuf::util::MessageToJsonString(test, &strJson, options);
        std::cout << "google: " << strJson << std::endl;
    }
    return 0;
}

以上代码中输出为：

json2pb: {"a":"aaa","b":"","c":""}
google: {"a":"aaa"}

brpc版本：1.12.1