replacing the NullCulprit class by None

appengine/findit/crash/crash_pipeline.py

 # Copyright 2016 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.
 
 import copy
 import json
 import logging
 
 from common import appengine_util
 from common import pubsub_util
@@ skipping 102 matching lines @@
     analysis = self._findit.GetAnalysis(self._crash_identifiers)
 
     # Update the model's status to say we're in the process of doing analysis.
     analysis.pipeline_status_path = self.pipeline_status_path()
     analysis.status = analysis_status.RUNNING
     analysis.started_time = time_util.GetUTCNow()
     analysis.findit_version = appengine_util.GetCurrentVersion()
     analysis.put()
 
     # Actually do the analysis.
-    result, tags = self._findit.FindCulprit(analysis).ToDicts()
+    culprit = self._findit.FindCulprit(analysis)
+    if culprit is not None:
+      result, tags = culprit.ToDicts()
+    else:
+      result = {'found': False}
+      tags = {
+          'found_suspects': False,
+          'found_project': False,
+          'found_components': False,
+          'has_regression_range': False,
+          'solution': None,
+      }
 
     # Update model's status to say we're done, and save the results.
     analysis.completed_time = time_util.GetUTCNow()
     analysis.result = result
     for tag_name, tag_value in tags.iteritems():
       # TODO(http://crbug.com/602702): make it possible to add arbitrary tags.
       if hasattr(analysis, tag_name):
         setattr(analysis, tag_name, tag_value)
     analysis.status = analysis_status.COMPLETED
     analysis.put()
@@ skipping 38 matching lines @@
     self._crash_identifiers = crash_identifiers
     self._client_id = client_id
 
   # TODO(http://crbug.com/659346): write coverage tests.
   # Arguments number differs from overridden method - pylint: disable=W0221
   def run(self): # pragma: no cover
     run_analysis = yield CrashAnalysisPipeline(
         self._client_id, self._crash_identifiers)
     with pipeline.After(run_analysis):
       yield PublishResultPipeline(self._client_id, self._crash_identifiers)