Fix case where we don't pass in a test base.

bin/au_test_harness/cros_au_test_harness.py

 #!/usr/bin/python
 
 # Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """This module runs a suite of Auto Update tests.
 
   The tests can be run on either a virtual machine or actual device depending
   on parameters given.  Specific tests can be run by invoking --test_prefix.
@@ skipping 218 matching lines @@
                  'specified if either is specified.')
     assert options.private_key and os.path.exists(options.private_key), \
         error_msg % 'private'
     assert options.public_key and os.path.exists(options.public_key), \
         error_msg % 'public'
 
   # Clean up previous work if requested.
   if options.clean: _CleanPreviousWork(options)
 
   # Make sure we have a log directory.
-  if not os.path.exists(options.test_results_root):
+  if options.test_results_root and not os.path.exists(
+      options.test_results_root):
     os.makedirs(options.test_results_root)
 
   # Pre-generate update modifies images by adding public keys to them.
   # Wrap try to make sure we clean this up before we're done.
   try:
     # Generate cache of updates to use during test harness.
     update_cache = _PregenerateUpdates(options)
     au_worker.AUWorker.SetUpdateCache(update_cache)
 
     my_server = dev_server_wrapper.DevServerWrapper(
@@ skipping 18 matching lines @@
     if options.public_key:
       cros_lib.Info('Cleaning up.  Removing keys added as part of testing.')
       target_directory = os.path.dirname(options.target_image)
       for key_manager in au_test.AUTest.public_key_managers:
         if key_manager.image_path.startswith(target_directory):
           key_manager.RemoveKeyFromImage()
 
 
 if __name__ == '__main__':
   main()