Fix case where there is nothing to uprev.

bin/cbuildbot.py

 #!/usr/bin/python
 
 # Copyright (c) 2010 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.
 
 """CBuildbot is wrapper around the build process used by the pre-flight queue"""
 
 import errno
 import optparse
@@ skipping 191 matching lines @@
     # Might not have entry if no matching ebuild.
     if repo_dictionary.has_key(repo_name):
       # May be many corresponding packages to a given git repo e.g. kernel).
       for package in repo_dictionary[repo_name]:
         revisions[package] = revision_tuple[1]
   return revisions.items()
 
 
 def _UprevFromRevisionList(buildroot, revision_list):
   """Uprevs based on revision list."""
+  if not revision_list:
+    print >> sys.stderr, 'No packages found to uprev'
+    return
   package_str = ''
   commit_str = ''
   for package, revision in revision_list:
     package_str += package + ' '
     commit_str += revision + ' '
   package_str = package_str.strip()
   commit_str = commit_str.strip()
 
   cwd = os.path.join(buildroot, 'src', 'scripts')
   RunCommand(['./cros_mark_as_stable',
@@ skipping 155 matching lines @@
       _UprevCleanup(buildroot)
   except:
     # something went wrong, cleanup (being paranoid) for next build
     if clobber:
       RunCommand(['sudo', 'rm', '-rf', buildroot], print_cmd=False)
     raise
 
 
 if __name__ == '__main__':
     main()