src/vs/workbench/contrib/audioCues/browser/observable.ts/LazyDerivedObserver/onLastObserverUnsubscribed
class LazyDerivedObserver:	protected override onLastObserverUnsubscribed(): void {
		/**
		 * We are not tracking changes anymore, thus we have to assume
		 * that our cache is invalid.
		*/
		this.hasValue = false;
		this.hadValue = false;
		this.value = undefined;
		for (const d of this._dependencies) {
			d.unsubscribe(this);
		}
		this._dependencies.clear();
	}