diff -r 5fa019ceb499 -r d55b71393907 mercurial/obsolete.py
--- a/mercurial/obsolete.py	Mon Apr 19 20:38:52 2021 -0400
+++ b/mercurial/obsolete.py	Mon Mar 29 01:52:06 2021 +0200
@@ -73,11 +73,14 @@
 import struct
 
 from .i18n import _
+from .node import (
+    bin,
+    hex,
+)
 from .pycompat import getattr
 from .node import (
     bin,
     hex,
-    nullid,
 )
 from . import (
     encoding,
@@ -526,14 +529,14 @@
                 children.setdefault(p, set()).add(mark)
 
 
-def _checkinvalidmarkers(markers):
+def _checkinvalidmarkers(repo, markers):
     """search for marker with invalid data and raise error if needed
 
     Exist as a separated function to allow the evolve extension for a more
     subtle handling.
     """
     for mark in markers:
-        if nullid in mark[1]:
+        if repo.nullid in mark[1]:
             raise error.Abort(
                 _(
                     b'bad obsolescence marker detected: '
@@ -727,7 +730,7 @@
             return []
         self._version, markers = _readmarkers(data)
         markers = list(markers)
-        _checkinvalidmarkers(markers)
+        _checkinvalidmarkers(self.repo, markers)
         return markers
 
     @propertycache
@@ -761,7 +764,7 @@
             _addpredecessors(self.predecessors, markers)
         if self._cached('children'):
             _addchildren(self.children, markers)
-        _checkinvalidmarkers(markers)
+        _checkinvalidmarkers(self.repo, markers)
 
     def relevantmarkers(self, nodes):
         """return a set of all obsolescence markers relevant to a set of nodes.