When branch is not correctly set, it would throw an exception.

gclient_scm.py

 # Copyright (c) 2009 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.
 
 """Gclient-specific SCM-specific operations."""
 
 import logging
 import os
 import posixpath
 import re
@@ skipping 556 matching lines @@
   def _CheckMinVersion(self, min_version):
     (ok, current_version) = scm.GIT.AssertVersion(min_version)
     if not ok:
       raise gclient_utils.Error('git version %s < minimum required %s' %
                                 (current_version, min_version))
 
   def _GetCurrentBranch(self):
     # Returns name of current branch
     # Returns None if inside a (no branch)
     tokens = self._Run(['branch']).split()
+    if not '*' in tokens:
+      return None
     branch = tokens[tokens.index('*') + 1]
     if branch == '(no':
       return None
     return branch
 
   def _Run(self, args, cwd=None, redirect_stdout=True):
     # TODO(maruel): Merge with Capture or better gclient_utils.CheckCall().
     if cwd is None:
         cwd = self.checkout_path
     stdout = None
@@ skipping 272 matching lines @@
       print("\n________ couldn't run \'%s\' in \'%s\':\nThe directory "
             "does not exist."
             % (' '.join(command), path))
       # There's no file list to retrieve.
     else:
       scm.SVN.RunAndGetFileList(options, command, path, file_list)
 
   def FullUrlForRelativeUrl(self, url):
     # Find the forth '/' and strip from there. A bit hackish.
     return '/'.join(self.url.split('/')[:4]) + url