What does this notation mean in C#?

Question

C++ / C#

Hello everyone, please help me with the following code:

private static string GetUserAgent(this HttpRequestMessage request)
            => request.Headers?.UserAgent?.ToString() ?? string.Empty;

What do the question marks mean in this case?
That the given expression can be null or something else?

Answer 1

Such a Headers?.UserAgent entry is a Null Propagation - if Headers == null the expression will return null (without the ? it would be NRE)
value ?? string.Empty is comparing value with null - if value != null then return value, otherwise return string.Empty

Answer 2

In addition to the above

///
// Метод возвращает UserAgent из запроса или пустую строку. Производится проверка на пустое значение Headers и UserAgent
///
private static string GetUserAgent(this HttpRequestMessage request)
            => request.Headers?.UserAgent?.ToString() ?? string.Empty;