This happens when you are not connected to any project in Connect window or project you connected to in Connect window is not configured for Multiplayer

How we can reproduce it using the example you attached:
1 Open attached project
2 Press Play
3 Press Enable Match Maker
4 Press Create Internet Match
Actual result: you will get non descriptive error in console:
" Invalid string passed into NetworkAccessToken ctor, exception:[System.ArgumentNullException: Argument cannot be null.
Parameter name: s "

Expected result: that error should be descriptive, something like "Make sure that project you connected to in the Connect window is Configured for Multiplayer "