[PATCH 2 of 6] revset: fix a crash with 'wdir() and merge()'

[Matt Harbison]

# HG changeset patch
# User Matt Harbison <matt_harbison at yahoo.com>
# Date 1435712708 14400
#      Tue Jun 30 21:05:08 2015 -0400
# Node ID e96033df31a3e45b1a0eecd793725c6aa9be7c14
# Parent  b912314a97b6f067c5bc4ee59c268489bfd0db11
revset: fix a crash with 'wdir() and merge()'

The crash was "TypeError: expected string or Unicode object, NoneType found"
down in revlog.parentrevs().

diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -1235,7 +1235,13 @@
     # i18n: "merge" is a keyword
     getargs(x, 0, 0, _("merge takes no arguments"))
     cl = repo.changelog
-    return subset.filter(lambda r: cl.parentrevs(r)[1] != -1)
+
+    def filter(r):
+        if r is None:
+            return len(repo[r].parents()) > 1
+        return cl.parentrevs(r)[1] != -1
+
+    return subset.filter(filter)
 
 def branchpoint(repo, subset, x):
     """``branchpoint()``
diff --git a/tests/test-merge-default.t b/tests/test-merge-default.t
--- a/tests/test-merge-default.t
+++ b/tests/test-merge-default.t
@@ -59,6 +59,13 @@
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     a
   
+  $ hg log -r 'wdir() and merge()'
+  changeset:   4:f25cbe84d8b3+
+  parent:      4:f25cbe84d8b3
+  parent:      2:2d95304fed5d
+  user:        test
+  date:        * (glob)
+  
   $ hg commit -mm1
 
 Should succeed - 2 heads: