Don’t add an href to links that don’t already have one

Addresses #3889

Author: dragonstyle

src/resources/projects/website/navigation/quarto-nav.js

@@ -180,7 +180,9 @@ window.document.addEventListener("DOMContentLoaded", function () {
   if (window.location.protocol !== "file:") {
     const links = window.document.querySelectorAll("a");
     for (let i = 0; i < links.length; i++) {
-      links[i].href = links[i].href.replace(/\/index\.html/, "/");
+      if (links[i].href) {
+        links[i].href = links[i].href.replace(/\/index\.html/, "/");
+      }
     }
 
     // Fixup any sharing links that require urls