--- a/mercurial/match.py	Mon Jan 07 15:25:41 2019 -0800
+++ b/mercurial/match.py	Mon Jan 07 19:03:23 2019 -0500
@@ -48,7 +48,7 @@
 
     for kind, pat, source in kindpats:
         if kind == 'set':
-            if not ctx:
+            if ctx is None:
                 raise error.ProgrammingError("fileset expression with no "
                                              "context")
             matchers.append(ctx.matchfileset(pat, badfn=badfn))