diff -r 29f52e7966dd -r aa849cf5d089 mercurial/obsutil.py
--- a/mercurial/obsutil.py	Tue Oct 17 16:54:31 2017 +0200
+++ b/mercurial/obsutil.py	Wed Oct 18 15:38:51 2017 +0200
@@ -822,7 +822,7 @@
     # Date
     dates = markersdates(markers)
 
-    if verbose:
+    if dates and verbose:
         min_date = min(dates)
         max_date = max(dates)