diff -r ad878e3f282b -r 728d89f6f9b1 mercurial/logcmdutil.py
--- a/mercurial/logcmdutil.py	Tue Mar 30 02:33:12 2021 +0200
+++ b/mercurial/logcmdutil.py	Tue Mar 30 02:32:30 2021 +0200
@@ -14,6 +14,7 @@
 from .i18n import _
 from .node import (
     nullid,
+    nullrev,
     wdirid,
     wdirrev,
 )
@@ -82,7 +83,7 @@
     If diff.merge is enabled, an overlayworkingctx of the auto-merged parents will be returned.
     """
     repo = ctx.repo()
-    if repo.ui.configbool(b"diff", b"merge") and ctx.p2().node() != nullid:
+    if repo.ui.configbool(b"diff", b"merge") and ctx.p2().rev() != nullrev:
         # avoid cycle context -> subrepo -> cmdutil -> logcmdutil
         from . import context