Problem with title and selectedTitle properties in Storyboard

[rlaurb]

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What did you do?

Added a SkyFloatingTextField to a storyboard. Specified a non-nil value for either/both the 'title' attribute or the 'selectedTitle' attribute.

What did you expect to happen?

The storyboard would compile without error or warning.

What happened instead?

file:///Users/rlaurb/Projects/MorningSugar/MorningSugar/Base.lproj/Main.
storyboard: warning: IB Designables: Ignoring user defined runtime attribute for
key path "title" on instance of "UITextField". Hit an exception when attempting
to set its value: [<UITextField 0x7f910e81b000> setValue:forUndefinedKey:]: this
class is not key value coding-compliant for the key title.

Environment

MacOS 10.15.4, Xcode 11.4 doing iOS development with storyboards.

Xcode Version: 11.4
SkyFloatingLabelTextField Version: 3.8.0
Deployment Target: iOS 13.0+
Base SDK: iOA 13.4
Method of Integration: SwiftPM

Project that demonstrates the issue

From my research, I think the problem is that these fields have type String? but are not overrides of existing Obj-C properties. I.e., IB seems to have problems with Swift Optionals that are not backed with Objc objects.