Console warning in dev mode: UNSAFE_componentWillMount is considered legacy

[victorlin]

This appears on any page defined in static-site/. Full text:

Warning: Using UNSAFE_componentWillMount in strict mode is not recommended and may indicate bugs in your code. See https://reactjs.org/link/unsafe-component-lifecycles for details.

• Move code with side effects to componentDidMount, and set initial state in the constructor.

Please update the following components: SideEffect(NullComponent)

[victorlin]

I took a quick look and can't seem to figure out where this is coming from. componentWillMount is not used in our code, so it's likely from some downstream dependency.