Pass a dict when no extra_headers is specified to upload.py.

rietveld.py

 # Copyright (c) 2011 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.
 """Defines class Rietveld to easily access a rietveld instance.
 
 Security implications:
 
 The following hypothesis are made:
 - Rietveld enforces:
   - Nobody else than issue owner can upload a patch set
@@ skipping 30 matching lines @@
 class Rietveld(object):
   """Accesses rietveld."""
   def __init__(self, url, email, password, extra_headers=None):
     self.issue = None
     self.url = url
     if email and password:
       get_creds = lambda: (email, password)
       self.rpc_server = upload.HttpRpcServer(
             self.url,
             get_creds,
-            extra_headers=extra_headers)
+            extra_headers=extra_headers or {})
     else:
       self.rpc_server = upload.GetRpcServer(url, email)
     self._xsrf_token = None
     self._xsrf_token_time = None
 
   def xsrf_token(self):
     if (not self._xsrf_token_time or
         (time.time() - self._xsrf_token_time) > 30*60):
       self._xsrf_token_time = time.time()
       self._xsrf_token = self.get(
@@ skipping 143 matching lines @@
         if retry >= (maxtries - 1):
           raise
         if not 'Name or service not known' in e.reason:
           # Usually internal GAE flakiness.
           raise
       # If reaching this line, loop again. Uses a small backoff.
       time.sleep(1+maxtries*2)
 
   # DEPRECATED.
   Send = get