What version of protobuf and what language are you using?

Version: 3.12.0-rc-1
Language: Java

What operating system (Linux, Windows, ...) and version?
Ubuntu 19.10

What runtime / compiler are you using (e.g., python version or gcc version)
openjdk version "1.8.0_252"

What did you do?
Steps to reproduce the behavior:

Define proto:

syntax = "proto3";

package mypkg;

enum V {
  A = 0;
  B = 1;
  C = 2;
}

message Msg {
  optional V v = 1;
}

In code:

import mypkg.Np.Msg;

import com.google.protobuf.TextFormat;
import com.google.protobuf.util.JsonFormat;

import java.lang.String;

public class Main {
    public static void main(String[] args) throws Exception {
        Msg withV = Msg.newBuilder().setV(mypkg.Np.V.B).build();
        // prints false, excepted true
        System.out.println(TextFormat.parse(withV.toString(), Msg.class).hasV());

        String js = JsonFormat.printer().print(withV);
        Msg.Builder b = Msg.newBuilder();
        JsonFormat.parser().merge(js, b);

        // prints false, excepted true
        System.out.println(b.build().hasV());
    }
}

Generated protos using protoc with --experimental_allow_proto3_optional.

What did you expect to see
When serializing the message withV above into ascii format or json, the optional field correctly shows up. The expectation is that v would be present when the json/ascii is parsed back.

What did you see instead?
However, when parsing both the json or text representation, the optional field gets ignored: hasV returns false in both cases, despite that the enum appears in the textual presentation.