Fix a crash in the owners check for a change without reviewers.

presubmit_canned_checks.py

 # 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.
 
 """Generic presubmit checks that can be reused by other presubmit checks."""
 
 import os as _os
 _HERE = _os.path.dirname(_os.path.abspath(__file__))
 
 
@@ skipping 778 matching lines @@
 
   owners_db = input_api.owners_db
   owner_email, reviewers = _RietveldOwnerAndReviewers(
       input_api,
       owners_db.email_regexp,
       approval_needed=input_api.is_committing)
 
   owner_email = owner_email or input_api.change.author_email
 
   if author_counts_as_owner and owner_email:
-    reviewers_plus_owner = set([owner_email]).union(reviewers or set())
+    reviewers_plus_owner = set([owner_email]).union(reviewers)
     missing_files = owners_db.files_not_covered_by(affected_files,
         reviewers_plus_owner)
   else:
     missing_files = owners_db.files_not_covered_by(affected_files, reviewers)
 
   if missing_files:
     output_list = [
         output('Missing %s for these files:\n    %s' %
                (needed, '\n    '.join(missing_files)))]
     if not input_api.is_committing:
@@ skipping 16 matching lines @@
 
 
 def _RietveldOwnerAndReviewers(input_api, email_regexp, approval_needed=False):
   """Return the owner and reviewers of a change, if any.
 
   If approval_needed is True, only reviewers who have approved the change
   will be returned.
   """
   issue_props = _GetRietveldIssueProps(input_api, True)
   if not issue_props:
-    return None, None
+    return None, set()
 
   if not approval_needed:
     return issue_props['owner_email'], set(issue_props['reviewers'])
 
   owner_email = issue_props['owner_email']
 
   def match_reviewer(r):
     return email_regexp.match(r) and r != owner_email
 
   messages = issue_props.get('messages', [])
@@ skipping 160 matching lines @@
     snapshot("checking description")
     results.extend(input_api.canned_checks.CheckChangeHasDescription(
         input_api, output_api))
     results.extend(input_api.canned_checks.CheckDoNotSubmitInDescription(
         input_api, output_api))
     snapshot("checking do not submit in files")
     results.extend(input_api.canned_checks.CheckDoNotSubmitInFiles(
         input_api, output_api))
   snapshot("done")
   return results