diff -r 656ac240f392 -r 638a241202a3 mercurial/formatter.py
--- a/mercurial/formatter.py	Sat Mar 24 01:30:50 2018 -0400
+++ b/mercurial/formatter.py	Thu Mar 15 21:49:33 2018 +0900
@@ -517,6 +517,9 @@
             return None
         return get(self, context, mapping, key)
 
+    def populatemap(self, context, origmapping, newmapping):
+        return {}
+
     def _getsome(self, context, mapping, key):
         v = mapping.get(key)
         if v is not None: