diff -r 335e19c6b7fa -r 05c13e5aa9ec mercurial/context.py
--- a/mercurial/context.py	Wed Mar 21 23:36:11 2018 +0530
+++ b/mercurial/context.py	Thu Mar 29 09:34:17 2018 -0700
@@ -415,7 +415,7 @@
     """A changecontext object makes access to data related to a particular
     changeset convenient. It represents a read-only context already present in
     the repo."""
-    def __init__(self, repo, changeid=''):
+    def __init__(self, repo, changeid='.'):
         """changeid is a revision number, node, or tag"""
 
         # since basectx.__new__ already took care of copying the object, we