ZMQ connection never sending 'Fmi2Instantiate'

[sagilar]

I just realized that the two-way connection of unifmu with ZMQ is never sending the 'Fmi2Instantiate' message (on its FMI2 version, probably also on its FMI3 version).

The order of the messages sent for initialization:

1. Fmi2SetupExperiment
2. Fmi2EnterInitializationMode
3. Fmi2ExitInitializationMode

But Fmi2Instantiate is never called, which should come first (before Fmi2SetupExperiment). This was probably designed since unifmu was intended to contain the white-box Model and not a black-box FMU on the model backend side.

The template for Python is indeed empty:

if group == "Fmi2Instantiate":
            result = Fmi2EmptyReturn()

The template for Java has no case for 'Fmi2Instantiate' and the template for C# is also empty:

case Fmi2Command.CommandOneofCase.Fmi2Instantiate:
                        {
                            var result = new Fmi2EmptyReturn();
                            message = result;
                        }
                        break;

According to this, the Model class (or any other black-box FMU) should be instantiated when the message 'Fmi2Instantiate' arrives. It wouldn't affect the overall functionality of the backend.