Warning "Expression of type UIViewController? is unused" in Xcode 8/Swift 3

Hello everyone! I'm new to Swift and encountered an unclear warning in Xcode 8 when working with iOS 10. I have simple code that shows a controller via storyboard:\n\n```swift\nlet storyboard = UIStoryboard(name: "Main", bundle: nil)\nlet secondVC = storyboard.instantiateViewController(withIdentifier: "SecondViewController")\nself.present(secondVC, animated: true, completion: nil)\n```\n\nEverything works, but Xcode gives a yellow warning on the second line: "Expression of type 'UIViewController?' is unused". I understand this is a warning about an unused value, but I am using secondVC in the next line! What am I doing wrong? This didn't happen before with Swift 2. How should I write this code correctly without the warning? I tried adding an exclamation mark after instantiateVie