[AAASM-4317] 🐛 (docs/theme): Guard inline new URL() against empty template value

docs/_overrides/main.html

@@ -40,8 +40,20 @@
       // above it. Resolving the bare relative `base_url` against `location`
       // yields an absolute URL; popping only the page's last path segment (the
       // previous approach) 404s on deep pages.
-      var versionRoot = new URL("{{ base_url }}/", window.location);
-      var versionsUrl = new URL("../versions.json", versionRoot).toString();
+      //
+      // AAASM-4317: guard the URL constructors so that a malformed or empty
+      // template value (e.g. a stray build variant where `base_url` renders
+      // blank) cannot throw `TypeError: Failed to construct 'URL': Invalid URL`
+      // and leave a visible page-load error in the console. On failure we keep
+      // the static fallback copy that is already rendered above.
+      var versionRoot;
+      var versionsUrl;
+      try {
+        versionRoot = new URL("{{ base_url }}/", window.location);
+        versionsUrl = new URL("../versions.json", versionRoot).toString();
+      } catch (e) {
+        return;
+      }
 
       // The current version id is the last path segment of the deploy root.
       var current =

docs/_overrides/partials/javascripts/outdated.html

@@ -7,8 +7,11 @@
   `..`, which is not an absolute URL, so `new URL("..")` throws
   `TypeError: Failed to construct 'URL': Invalid URL` on every page load.
 
-  The only change here is passing `location` as the base so the relative
-  `base_url` resolves against the current page. Behaviour is otherwise identical
-  to Material's generated script.
+  Passing `location` as the base resolves the relative `base_url` against the
+  current page. The try/catch (AAASM-4317) is defense-in-depth: any future
+  template regression that renders `base_url` as an unparseable value (e.g. an
+  empty string on a build variant that omits `site_url`) will silently no-op
+  the outdated banner instead of surfacing a page-load TypeError. Behaviour is
+  otherwise identical to Material's generated script.
 -#}
-<script>var el=document.querySelector("[data-md-component=outdated]"),base=new URL("{{ base_url }}",location),outdated=__md_get("__outdated",sessionStorage,base);!0===outdated&&el&&(el.hidden=!1)</script>
+<script>try{var el=document.querySelector("[data-md-component=outdated]"),base=new URL("{{ base_url }}",location),outdated=__md_get("__outdated",sessionStorage,base);!0===outdated&&el&&(el.hidden=!1)}catch(e){}</script>