Skip entries with missing abs_url from sitemap

Author: Oleh Prypin

mkdocs/templates/sitemap.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
 {%- for file in pages -%}
-    {% if not file.page.is_link %}
+    {% if not file.page.is_link and (file.page.abs_url or file.page.canonical_url) %}
     <url>
          <loc>{% if file.page.canonical_url %}{{ file.page.canonical_url|e }}{% else %}{{ file.page.abs_url|e }}{% endif %}</loc>
          {% if file.page.update_date %}<lastmod>{{file.page.update_date}}</lastmod>{% endif %}