Using await in an async handler returns undefined to clients

[Ganitzsh]

Hello,

I have an issue with empty response to clients when using await within async functions.

Here is my proto:

syntax = "proto3";

package user;

service User {
  rpc GetUserFullName(GetUserFullNameRequest) returns (GetUserFullNameResponse) {}
}

message GetUserFullNameRequest {
  string user_id = 1;
}

message GetUserFullNameResponse {
  string full_name = 1;
}

I have this handler:

import { UserModel } from 'mongoose/models';

async function getUserFullName(ctx) {
  const user = await UserModel.findById(ctx.req.userId);

  console.log(user); // The user is properly retrieved

   ctx.res = { fullName: `${user.firstName} ${user.lastName}` };
}

Very simple so far, but upon calling it with a client generated with grpc-caller I get this error:

const response = await userServiceClient.getUserFullName({
  userId: args.userId,
});

Error: 13 INTERNAL: Cannot read property 'fullName' of undefined
    at Object.callErrorFromStatus (/node_modules/@grpc/grpc-js/src/call.ts:81:24)
    at Object.onReceiveStatus (/node_modules/@grpc/grpc-js/src/client.ts:343:36)
    at Object.onReceiveStatus (/node_modules/@grpc/grpc-js/src/client-interceptors.ts:462:34)
    at Object.onReceiveStatus (//node_modules/@grpc/grpc-js/src/client-interceptors.ts:424:48)
    at /node_modules/@grpc/grpc-js/src/call-stream.ts:323:24
    at processTicksAndRejections (node:internal/process/task_queues:78:11) {
  code: 13,
  details: "Cannot read property 'fullName' of undefined",
  metadata: Metadata { internalRepr: Map(0) {}, options: {} }
}

But, when I change my hander to the following:

async function getUserFullName(ctx) {
  ctx.res = (async () => {
    const user = await UserModel.findById(ctx.req.userId);
    return { fullName: `${user.firstName} ${user.lastName}` };
  })()
}

It works fine, but I'm not sure why. Is it due to the UNARY nature of the call?