fix(dom): `querySelector` and friends return empty when selector is empty

src/dom/htmlelement.spec.ts

@@ -609,6 +609,11 @@ describe("HtmlElement", () => {
 			const el = root.querySelector("foobar");
 			expect(el).toBeNull();
 		});
+
+		it("should return null if selector is empty", () => {
+			const el = root.querySelector("");
+			expect(el).toBeNull();
+		});
 	});
 
 	describe("querySelectorAll()", () => {
@@ -636,6 +641,11 @@ describe("HtmlElement", () => {
 			const el = root.querySelectorAll("missing");
 			expect(el).toEqual([]);
 		});
+
+		it("should return [] if selector is empty", () => {
+			const el = root.querySelectorAll("");
+			expect(el).toEqual([]);
+		});
 	});
 
 	describe("visitDepthFirst()", () => {

src/dom/htmlelement.ts

@@ -426,6 +426,9 @@ export class HtmlElement extends DOMNode {
 	private *querySelectorImpl(
 		selectorList: string
 	): IterableIterator<HtmlElement> {
+		if (!selectorList) {
+			return;
+		}
 		for (const selector of selectorList.split(/,\s*/)) {
 			const pattern = new Selector(selector);
 			yield* pattern.match(this);