How to use optional?

[ccll ddd]

when I use grpc in python.

```

message Response {

    bool is_admin = 1;

    repeated string names = 2;

}

```

grpc server return a False for is_admin, and null value for names;

But in client, I use json_format.MessageToDict.

if I don't use including_default_value_fields=True, the is_admin will not found in dict.

{}

If I use including_default_value_fields=True, the names is a list.But I don't need names.

{"is_admin": False, "names": []}

what can i do ?