--- a/mercurial/revlogutils/deltas.py	Thu Apr 20 09:23:58 2023 -0400
+++ b/mercurial/revlogutils/deltas.py	Wed Apr 19 16:59:03 2023 +0200
@@ -684,6 +684,9 @@
         yield None
         return
 
+    if target_rev is None:
+        target_rev = len(revlog)
+
     if (
         cachedelta is not None
         and nullrev == cachedelta[0]