--- a/mercurial/changegroup.py	Thu Aug 09 12:03:39 2018 -0400
+++ b/mercurial/changegroup.py	Tue Aug 07 10:24:49 2018 -0700
@@ -604,9 +604,9 @@
     def _close(self):
         # Ellipses serving mode.
         self._clrevtolocalrev.clear()
-        if self._nextclrevtolocalrev:
+        if self._nextclrevtolocalrev is not None:
             self._clrevtolocalrev = self._nextclrevtolocalrev
-            self._nextclrevtolocalrev.clear()
+            self._nextclrevtolocalrev = None
         self._changelogdone = True
 
         return closechunk()