C#: why Session = null, but not always?

Question

C++ / C#

Hi all!
Web project in VisualStudio 2013. Functionality partly on .aspx files, partly on a web service (.asmx). So the problem is that the Session object is available in the .aspx.cs files, and without any imports. And in the web service file Session == null.
Tell me why there is no single session. I understand that the mechanism behind .aspx creates this object somewhere and initializes it.

Answer 1

session is initialized separately naturally. And on the service, most likely it is checked in order not to let unlogged users where it is not necessary.