Can anyone please help me figure out how to fix this?
For anyone interested, I found out the problem to be that the game instance class in project settings was null, changing it to my game instance work.
Oh so you solved it yourself 
“NewObject” is function that instantiates new UObject (Same as SpawnActor for Actors) error say that class inputed was null (which figured where it was set to null) ;] I think this could be consider design flaw on UE4 side, it should be default UGameInstace and never be able to set it to null in editor.