--- a/mercurial/context.py	Mon Aug 28 16:49:41 2017 -0700
+++ b/mercurial/context.py	Mon Aug 28 16:58:59 2017 -0700
@@ -2371,7 +2371,7 @@
         for f in self._files:
             if not managing(f):
                 added.append(f)
-            elif self[f]:
+            elif f in self:
                 modified.append(f)
             else:
                 removed.append(f)