'Why do I keep getting a white screen when loading a SKS in Swift?

                  let gameOver = SKScene(fileNamed: "GameOverScene") as? GameOverScene
                  gameOver?.score = self.score
                  self.view!.presentScene(gameOver)
                  
                }

Here is the code that I have been having problems with. It clears all the nodes (which is good) but shows me a blank white screen. If I swap the ?s to !s then I get Thread 1 signal SIGABRT. Does anyone know how to fix this? This happens on Xcode simulator and on my iPad.



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