contrib/perf.py

--- a/contrib/perf.py	Wed Nov 06 14:13:19 2019 +0100
+++ b/contrib/perf.py	Sat Nov 02 14:45:57 2019 +0100
@@ -820,6 +820,7 @@
     if util.safehasattr(cl, b'clearcaches'):
         cl.clearcaches()
     elif util.safehasattr(cl, b'_nodecache'):
+        # <= hg-5.2
         from mercurial.node import nullid, nullrev
 
         cl._nodecache = {nullid: nullrev}