src/vs/workbench/contrib/search/browser/searchWidget.ts/SearchWidget/validateSearchInput
class SearchWidget:	private validateSearchInput(value: string): IMessage | null {
		if (value.length === 0) {
			return null;
		}
		if (!this.searchInput.getRegex()) {
			return null;
		}
		try {
			new RegExp(value, 'u');
		} catch (e) {
			return { content: e.message };
		}

		return null;
	}