--- a/hgext/convert/common.py	Wed Sep 10 11:01:47 2014 -0400
+++ b/hgext/convert/common.py	Mon May 26 11:53:12 2014 -0400
@@ -109,6 +109,13 @@
         """Return the commit object for version"""
         raise NotImplementedError
 
+    def numcommits(self):
+        """Return the number of commits in this source.
+
+        If unknown, return None.
+        """
+        return None
+
     def gettags(self):
         """Return the tags as a dictionary of name: revision