How to set back button text in Swift

How do you remove the back button text.

Current back button:

< Back

Desired back button:

< AnythingElse

None of these have worked:

self.navigationItem.backBarButtonItem?.title = "Back"
self.backItem?.title = ""
self.navigationController?.navigationBar.backItem?.title = ""
self.navigationItem.backBarButtonItem?.title = ""
self.navigationController?.navigationItem.backBarButtonItem?.title="Back"
self.navigationController?.navigationBar.backItem?.title = ""
self.navigationController?.navigationItem.backBarButtonItem?.title