Incorrect generated encoder/decoder for empty message in RPC endpoints

[Merlin04]

With a simple .proto file like this:

syntax = "proto3";

message Empty {}

service Test {
  rpc Ping (Empty) returns (Empty);
}

the generated .ml file contains these functions for the Empty message:

let rec encode_pb_empty (v:empty) encoder = 
()

let rec decode_pb_empty d =
  match Pbrt.Decoder.key d with
  | None -> ();
  | Some (_, pk) -> 
    Pbrt.Decoder.unexpected_payload "Unexpected fields in empty message(empty)" pk

however, the encoder/decoder functions for the Ping endpoint in the Server and Client modules are incorrectly(?) defined as

fun () enc -> Pbrt.Encoder.empty_nested enc
fun d -> Pbrt.Decoder.empty_nested d

which produce an error when given a value encoded/decoded with the functions for the empty message type:

# let e = Pbrt.Encoder.create ();;
val e : Pbrt.Encoder.t = <abstr>
# encode_pb_empty () e;;
- : empty = ()
# let b = Pbrt.Encoder.to_bytes e;;
val b : bytes = Bytes.of_string ""
# Pbrt.Decoder.of_bytes b |> Pbrt.Decoder.empty_nested;;
Exception: Pbrt.Decoder.Failure(Incomplete)