Don't try to strip NoneType expect_dirs

expect_tests/type_definitions.py

 # Copyright 2014 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.
 
 import inspect
 import os
 import re
 
 from collections import namedtuple
 
@@ skipping 170 matching lines @@
     """
     breakpoints = breakpoints or []
     if not breakpoints or break_funcs:
       for f in (break_funcs or (func_call.func,)):
         if hasattr(f, 'im_func'):
           f = f.im_func
         breakpoints.append((f.func_code.co_filename,
                             f.func_code.co_firstlineno,
                             f.func_code.co_name))
 
-    expect_dir = expect_dir.rstrip('/')
+    if expect_dir:
+      expect_dir = expect_dir.rstrip('/')
     return super(Test, cls).__new__(cls, name, func_call, expect_dir,
                                     expect_base, ext, covers, breakpoints)
 
 
   @staticmethod
   def covers_obj(obj):
     test_file = inspect.getabsfile(obj)
     covers = [test_file]
     match = Test.TEST_COVERS_MATCH.match(test_file)
     if match:
@@ skipping 222 matching lines @@
         print 'UNHANDLED:', obj
       return Failure()
 
     def finalize(self, aborted):
       """Called after __call__() has been called for all results.
 
       @param aborted: True if the user aborted the run.
       @type aborted: bool
       """
       pass