This is not the Django repository. The task is to generate a patch for the Django sitemaps issue. Based on the problem statement and the hint, I need to generate the patch. Let me create the fix based on the information provided:

The issue is in `django/contrib/sitemaps/__init__.py` at the `get_latest_lastmod` method. When a sitemap has no items but has a callable `lastmod`, it raises a `ValueError` because `max()` is called on an empty sequence.

The hint suggests using the default argument of `max()`. Here's the patch:

--- a/django/contrib/sitemaps/__init__.py
+++ b/django/contrib/sitemaps/__init__.py
@@ -167,7 +167,7 @@ class Sitemap:
         if not hasattr(self, "lastmod"):
             return None
         if callable(self.lastmod):
-            try:
-                return max([self.lastmod(item) for item in self.items()])
-            except TypeError:
+            try:
+                return max([self.lastmod(item) for item in self.items()], default=None)
+            except TypeError:
                 return None
         else:
             return self.lastmod