Visual Studio抱怨以下内容：

public RelayCommand SendRegistrationCommand { get; private set; }
public async void SendRegistration()
{
    HttpClient client = new HttpClient();
    var response = await client.GetStringAsync("url");

    // ... todo
}

Cannot await 'System.Threading.Tasks.Task<string>'

我以为我以前做过,GetStringAsync不等待？