gdscript bindings: optional vector2 tries to decode as if required

[cmdrk]

message entity {
    required uint64  id       = 1;
    required vector2 position = 2;
    optional vector2 velocity = 3; // doesn't work as OPTIONAL and VECTOR2 in this message. investigate!
    required float   rotation = 4;
}

In Godot:

Invalid call. Nonexistent function 'get_x' in base 'Nil'.

Workaround to just require velocity or remove it from the message altogether. Not ideal!