diff -r cc33deae66a1 -r 5b9de38a0356 mercurial/commit.py
--- a/mercurial/commit.py	Fri Sep 10 14:37:03 2021 -0400
+++ b/mercurial/commit.py	Fri Sep 10 14:57:00 2021 -0400
@@ -389,6 +389,7 @@
     text = fctx.data()
     if (
         fparent2 != repo.nullid
+        or fparent1 == repo.nullid
         or meta
         or flog.cmp(fparent1, text)
         or force_new_node