Add checks to GitSanityChecks (upstream branch or current branch can be None)

git_cl.py

 #!/usr/bin/env python
 # 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.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld."""
 
 from distutils.version import LooseVersion
@@ skipping 623 matching lines @@
         self._remote = (remote, branch)
       elif branch.startswith('refs/branch-heads/'):
         self._remote = (remote, branch.replace('refs/', 'refs/remotes/'))
       else:
         self._remote = (remote, 'refs/remotes/%s/%s' % (remote, branch))
     return self._remote
 
   def GitSanityChecks(self, upstream_git_obj):
     """Checks git repo status and ensures diff is from local commits."""
 
+    if upstream_git_obj is None:
+      if self.GetBranch() is None:
+        print >> sys.stderr, (
+            'ERROR: unable to dertermine current branch (detached HEAD?)')
+      else:
+        print >> sys.stderr, (
+            'ERROR: no upstream branch')
+      return False
+
     # Verify the commit we're diffing against is in our current branch.
     upstream_sha = RunGit(['rev-parse', '--verify', upstream_git_obj]).strip()
     common_ancestor = RunGit(['merge-base', upstream_sha, 'HEAD']).strip()
     if upstream_sha != common_ancestor:
       print >> sys.stderr, (
           'ERROR: %s is not in the current branch.  You may need to rebase '
           'your tracking branch' % upstream_sha)
       return False
 
     # List the commits inside the diff, and verify they are all local.
@@ skipping 2262 matching lines @@
         ('AppEngine is misbehaving and returned HTTP %d, again. Keep faith '
           'and retry or visit go/isgaeup.\n%s') % (e.code, str(e)))
 
 
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   colorama.init()
   sys.exit(main(sys.argv[1:]))