Ensure parent page is actually a page

hooks/nav.py

@@ -25,11 +25,14 @@ def children(page):
 
 def get_parent_page(page):
     if is_list_page(page) and len(page.parent.children) == 1:
-        parent_section = page.parent.parent
-        if parent_section:
-            return parent_section.children[0]
+        parent = page.parent.parent
+    else:
+        parent = page.parent
 
-    return page.parent
+    if parent is None:
+        return None
+
+    return parent.children[0]
 
 
 @jinja2.pass_context