src/vs/workbench/contrib/timeline/browser/timelinePane.ts/TimelinePane/ensureValidItems
class TimelinePane:	ensureValidItems() {
		// If we don't have any non-excluded timelines, clear the tree and show the loading message
		if (!this.hasVisibleItems || !this.timelineService.getSources().some(({ id }) => !this.excludedSources.has(id) && this.timelinesBySource.has(id))) {
			this.tree.setChildren(null, undefined);
			this._isEmpty = true;

			this.setLoadingUriMessage();

			return false;
		}

		return true;
	}