default enum value is omitted

[fiibbb]

Consider the following IDL

enum MyEnum {
  CASE_A = 0;
  CASE_B = 1;
}
message MyMsg {
  MyEnum my_value = 1;
}

When a MyMsg is sent to an HTTP client (in my case curl) over grpc-gateway with value set to CASE_A (0), the client seem to receive and empty json object with the field my_value omitted all together.
IE, we receive

{}

instead of

{
  "my_value": "CASE_A"
}

In jsonpb, we can set jsonpb.Marshaler.EmitDefaults to true to avoid this behavior. Is that also supported in grpc-gateway?

[tmc]

This is possible by supplying an option to NewServeMux via https://godoc.org/github.com/grpc-ecosystem/grpc-gateway/runtime#WithMarshalerOption