Looks like it's issue with the way the TabControl is being instantiated by the run time. It appears that the first time the SelectionChanged event is being raised the ContentTemplate is not quite ready to be accessed. If you run your code again and skip over the first access of ContentTemplate you'll see that in subsequent events you can access this property without the exception being thrown.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.