build(aio): fix warning about missing `<h1>`

Fixes #17549

aio/content/marketing/index.html

@@ -14,17 +14,19 @@
 
     <!-- CONTAINER -->
     <div class="homepage-container">
-      <!-- container content starts -->
-
       <div class="hero-headline no-toc">One framework.<br>Mobile &amp; desktop.</div>
       <a class="button hero-cta" href="guide/quickstart">Get Started</a>
-  </div><!-- CONTAINER END -->
-  </section>
+    </div>
 
+  </section>
 
 </header>
 
+<!-- MAIN CONTENT -->
 <article>
+
+  <h1 class="no-toc" style="display: none"></h1>
+
   <div class="home-rows">
 
     <!-- Announcement Bar -->
@@ -53,6 +55,7 @@
       </div>
     </div>
     <hr>
+
     <!-- Group 2 -->
     <div layout="row" layout-xs="column" class="home-row">
       <div class="text-container">
@@ -90,7 +93,6 @@
 
     <!-- Group 4 -->
     <div layout="row" layout-xs="column" class="home-row">
-
       <div class="text-container">
         <div class="text-block l-pad-top-2">
           <div class="text-headline">Loved by Millions</div>
@@ -107,7 +109,6 @@
 
     <!-- CTA CARDS -->
     <div layout="row" layout-xs="column" class="home-row">
-
       <a href="guide/quickstart">
         <div class="card">
           <img src="generated/images/marketing/home/code-icon.svg" height="70px">

aio/tools/transforms/angular-base-package/post-processors/h1-checker.js

@@ -34,5 +34,5 @@ function getText(h1) {
     (node.properties.ariaHidden === 'true' || node.properties['aria-hidden'] === 'true')
   ));
 
-  return toString(cleaned);
+  return cleaned ? toString(cleaned) : '';
 }

aio/tools/transforms/angular-base-package/post-processors/h1-checker.spec.js

@@ -69,4 +69,14 @@ describe('h1Checker postprocessor', () => {
     processor.$process([doc]);
     expect(doc.vFile.title).toEqual('What is Angular?');
   });
+
+  it('should not break if the h1 is empty (except for an aria-hidden anchor)', () => {
+    const doc = {
+      docType: 'a',
+      renderedContent: `
+        <h1><a aria-hidden="true"></a></h1>
+      `
+    };
+    expect(() => processor.$process([doc])).not.toThrow();
+  });
 });