Fix a coding error that was introduced in 26423.

gclient_scm.py

 # Copyright 2009 Google Inc.  All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
 #      http://www.apache.org/licenses/LICENSE-2.0
 #
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 33 matching lines @@
     self.relpath = relpath
     if self.relpath:
       self.relpath = self.relpath.replace('/', os.sep)
 
   def FullUrlForRelativeUrl(self, url):
     # Find the forth '/' and strip from there. A bit hackish.
     return '/'.join(self.url.split('/')[:4]) + url
 
   def RunCommand(self, command, options, args, file_list=None):
     # file_list will have all files that are modified appended to it.
-
-    file_list = file_list or []
+    if file_list is None:
+      file_list = []
 
     commands = {
       'cleanup':  self.cleanup,
       'export':   self.export,
       'update':   self.update,
       'revert':   self.revert,
       'status':   self.status,
       'diff':     self.diff,
       'pack':     self.pack,
       'runhooks': self.status,
@@ skipping 502 matching lines @@
                           xml_props_status)
         # Col 2
         if wc_status[0].getAttribute('wc-locked') == 'true':
           statuses[2] = 'L'
         # Col 3
         if wc_status[0].getAttribute('copied') == 'true':
           statuses[3] = '+'
         item = (''.join(statuses), file)
         results.append(item)
   return results