fix: ensure nullish expressions render empty text (#12898)

Author: trueadm

.changeset/unlucky-points-clap.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure nullish expressions render empty text

packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/utils.js

@@ -59,7 +59,13 @@ export function build_template_literal(values, visit, state) {
 						id,
 						create_derived(
 							state,
-							b.thunk(/** @type {Expression} */ (visit(node.expression, state)))
+							b.thunk(
+								b.logical(
+									'??',
+									/** @type {Expression} */ (visit(node.expression, state)),
+									b.literal('')
+								)
+							)
 						)
 					)
 				);

packages/svelte/tests/runtime-runes/samples/text-multiple-nullish-expression/_config.js

@@ -0,0 +1,5 @@
+import { test } from '../../test';
+
+export default test({
+	html: '<li></li>'
+});

packages/svelte/tests/runtime-runes/samples/text-multiple-nullish-expression/main.svelte

@@ -0,0 +1,4 @@
+<script>
+	function fn() {}
+</script>
+<li>{fn()}{null && fn()}</li>