If you want to pass nil arguments into your function, declare the arguments as optionals, like this:

func createImage( ... , answerAction: Bool, targetObject: Any?, actionName: Selector?) -> UIImageView {

Then, inside the function, you'll need to check if they're nil. Also, when you call the function, you'll need to include these arguments in the call, like:

let backgroundImage = customElements.createImage(... , answerAction: false, targetObject: nil, actionName: nil)

Alternatively, you can define default values for the parameters, like this:

func createImage( ... , answerAction: Bool, targetObject: Any = self, actionName: Selector = #selector(defaultAction)) -> UIImageView {

And then you'll need to implement defaultAction inside class CustomElements, like this:

@objc func defaultAction() { ... }

In this case, you can omit the last two parameters when calling the function, like:

let backgroundImage = customElements.createImage(... , answerAction: false)

You can also use both techniques, they aren't mutually excludent. Hope that has answered your question.