Maps should be serialized as a key-values according to [google protobuf specification](https://developers.google.com/protocol-buffers/docs/proto3#json). | Proto3 | JSON | JSON Example | Notes | | --- | --- | --- | --- | | `map<K,V>` | object | `{"k": v, …}` | All keys are converted to strings. | Currently they are serialized as a repeated list of messages.