using GET to pass params passes null object

Question

I have the following GET method in order to pass params to my API server(and get an instance of employee from database at the end), but when debugging, I have noticed that the parameter being passed is null. I'm assuming that I'm doing something wrong, but not sure what exactly.

The http error (of course) is : 500 (Internal Server Error) - System.NullReferenceException.

That's my Angular code:

getEmp(id: number): Observable < any > {
  let params: URLSearchParams = new URLSearchParams();
  params.set('id', id.toString());
  return this._http.get(AppSettings.getEmp, {
      search: params
    })
    .map((data: any) => data.json());
}

That's the subscriber:

getEmpService() {
  this._adminService.getOved(this.adminForm.value.id).subscribe((res) => {
    debugger;
    if (res) { ...
    }
  }, error => {
    console.log("failed");
  })
}

I can clearly see that the value is being sent on the client side is correct, but not sure what's happening from that moment

Angular Version : ^7.1.4