patch can be None in the exception, causing a secondary exception.

checkout.py

 # coding=utf8
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 """Manages a project checkout.
 
 Includes support for svn, git-svn and git.
 """
 
 import ConfigParser
@@ skipping 58 matching lines @@
   def filename(self):
     if self.patch:
       return self.patch.filename
 
   def __str__(self):
     out = []
     if self.filename:
       out.append('Failed to apply patch for %s:' % self.filename)
     if self.status:
       out.append(self.status)
-    out.append('Patch: %s' % self.patch.dump())
+    if self.patch:
+      out.append('Patch: %s' % self.patch.dump())
     return '\n'.join(out)
 
 
 class CheckoutBase(object):
   # Set to None to have verbose output.
   VOID = subprocess2.VOID
 
   def __init__(self, root_dir, project_name, post_processors):
     """
     Args:
@@ skipping 633 matching lines @@
   def revisions(self, rev1, rev2):
     return self.checkout.revisions(rev1, rev2)
 
   @property
   def project_name(self):
     return self.checkout.project_name
 
   @property
   def project_path(self):
     return self.checkout.project_path