Thread 1: signal SIGABRT when my code runs - swift

Question

Total Swift newbie here. I am trying to make two containers that span half of the view.heightAnchor.constraint with one function createhalfcontainer in order to make things neater. Whenever I run my code, I get the signal SIGABRT and despite extensive code review I can't seem to find out why.
class ViewController: UIViewController {
let iv = {() -> UIImageView in
let imageview = UIImageView(image: #imageLiteral(resourceName: "google"))
imageview.contentMode = UIViewContentMode.scaleAspectFit
return imageview
}()
let tv = {() -> UITextView in
let textview = UITextView()
textview.text = "I am going to work here soon."
textview.font = UIFont.boldSystemFont(ofSize: 16)
textview.textAlignment = NSTextAlignment.center
textview.isEditable = false
return textview
}()
func createhalfcontainer(within: UIView, direction:String, view: UIView)-> UIView{
let container = UIView()
container.translatesAutoresizingMaskIntoConstraints = false
within.translatesAutoresizingMaskIntoConstraints = false
container.heightAnchor.constraint(equalTo: view.heightAnchor,multiplier: 0.5).isActive = true
container.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
container.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
if direction == "up" {
container.topAnchor.constraint(equalTo:view.topAnchor).isActive = true
within.topAnchor.constraint(equalTo: container.topAnchor, constant: 100).isActive = true}
else {container.bottomAnchor.constraint(equalTo:view.bottomAnchor).isActive = true
within.bottomAnchor.constraint(equalTo: container.bottomAnchor, constant: 100).isActive = true}
within.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
within.trailingAnchor.constraint(equalTo: container.trailingAnchor).isActive = true
container.addSubview(within)
return container
}
override func viewDidLoad() {
super.viewDidLoad() //This instantiates the view object
let uppercontainer = self.createhalfcontainer(within: iv, direction: "up", view:view)
let bottomcontainer = self.createhalfcontainer(within: tv, direction: "bottom",view:view)
view.addSubview(uppercontainer)
view.addSubview(bottomcontainer)
}
}