--- a/tests/test-revset.t	Sun Aug 09 16:06:36 2015 +0900
+++ b/tests/test-revset.t	Sun Aug 09 16:09:41 2015 +0900
@@ -1144,6 +1144,20 @@
   4
   5
 
+no crash by empty group "()" while optimizing `or` operations
+
+  $ try --optimize '0|()'
+  (or
+    ('symbol', '0')
+    (group
+      None))
+  * optimized:
+  (or
+    ('symbol', '0')
+    None)
+  hg: parse error: missing argument
+  [255]
+
 test that chained `or` operations never eat up stack (issue4624)
 (uses `0:1` instead of `0` to avoid future optimization of trivial revisions)