diff -r b5e1283c0475 -r 6ad70879d2bd mercurial/simplemerge.py
--- a/mercurial/simplemerge.py	Fri Jan 07 22:23:44 2022 -0800
+++ b/mercurial/simplemerge.py	Fri Jan 07 23:29:19 2022 -0800
@@ -332,10 +332,10 @@
     return text
 
 
-def _picklabels(defaults, overrides):
+def _picklabels(overrides):
     if len(overrides) > 3:
         raise error.Abort(_(b"can only specify three labels."))
-    result = defaults[:]
+    result = [None, None, None]
     for i, override in enumerate(overrides):
         result[i] = override
     return result
@@ -501,9 +501,7 @@
     elif mode == b'other':
         lines = _resolve(m3, (2,))
     else:
-        name_a, name_b, name_base = _picklabels(
-            [localctx.path(), otherctx.path(), None], opts.get('label', [])
-        )
+        name_a, name_b, name_base = _picklabels(opts.get('label', []))
         if mode == b'mergediff':
             lines, conflicts = render_mergediff(m3, name_a, name_b, name_base)
         else: