allow empty <title> tags - fixes #2980 (#2988)

Author: Rich-Harris

src/compiler/compile/render-dom/wrappers/Title.ts

@@ -91,7 +91,10 @@ export default class TitleWrapper extends Wrapper {
 				);
 			}
 		} else {
-			const value = stringify((this.node.children[0] as Text).data);
+			const value = this.node.children.length > 0
+				? stringify((this.node.children[0] as Text).data)
+				: '""';
+
 			block.builders.hydrate.add_line(`document.title = ${value};`);
 		}
 	}

test/runtime/samples/head-title-empty/_config.js

@@ -0,0 +1,5 @@
+export default {
+	test({ assert, window }) {
+		assert.equal(window.document.title, '');
+	}
+};

test/runtime/samples/head-title-empty/main.svelte

@@ -0,0 +1,3 @@
+<svelte:head>
+	<title></title>
+</svelte:head>