Xcode 7 webkit causes thread 1: signal SIGABRT error

I downloaded Xcode 7 to my mac to make a web browser using the webkit feature. I started working on the basic layout, and it worked well. I then added the webkit element to my window, and when I tested it, I got this: [Image] The code that contains the error

I have tried many things such as checking the outlets, but nothing has worked. All help is appreciated.