[Findit] Make sure not use empty list or dict as default value.

appengine/findit/model/wf_swarming_task.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.
 
 from collections import defaultdict
 
 from google.appengine.ext import ndb
 
 from model.base_build_model import BaseBuildModel
 from model import analysis_status
 
 
 class WfSwarmingTask(BaseBuildModel):
   """Represents a swarming task for a failed step.
 
   'Wf' is short for waterfall.
   """
   # The id of the Swarming task scheduled or running on Swarming Server.
   task_id = ndb.StringProperty(indexed=False)
 
   # A dict to keep track of running information for each test:
   # number of total runs, number of each status (such as 'SUCCESS' or 'FAILED')
-  tests_statuses = ndb.JsonProperty(default={}, indexed=False, compressed=True)
+  tests_statuses = ndb.JsonProperty(indexed=False, compressed=True)
 
   # The status of the swarming task.
   status = ndb.IntegerProperty(
       default=analysis_status.PENDING, indexed=False)
 
   # The revision of the failed build.
   build_revision = ndb.StringProperty(indexed=False)
 
   # Time when the task is created.
   created_time = ndb.DateTimeProperty(indexed=True)
   # Time when the task is started.
   started_time = ndb.DateTimeProperty(indexed=False)
   # Time when the task is completed.
   completed_time = ndb.DateTimeProperty(indexed=False)
 
   # parameters need to be stored and analyzed later.
-  parameters = ndb.JsonProperty(default={}, indexed=False, compressed=True)
+  parameters = ndb.JsonProperty(indexed=False, compressed=True)
 
   @property
   def classified_tests(self):
     """Classification of tests into lists of reliable and flaky tests.
 
     example format would be:
     {
         'flaky_tests': ['test1', 'test2', ...],
         'reliable_tests': ['test3', ...],
         'unknown_tests': ['test4', ...]
@@ skipping 16 matching lines @@
   @staticmethod
   def _CreateKey(
       master_name, builder_name, build_number, step_name):  # pragma: no cover
     build_id = BaseBuildModel.CreateBuildId(
         master_name, builder_name, build_number)
     return ndb.Key('WfBuild', build_id, 'WfSwarmingTask', step_name)
 
   @staticmethod
   def Create(
       master_name, builder_name, build_number, step_name):  # pragma: no cover
-    return WfSwarmingTask(
+    task = WfSwarmingTask(
         key=WfSwarmingTask._CreateKey(
             master_name, builder_name, build_number, step_name))
+    task.parameters = task.parameters or {}
+    task.tests_statuses = task.tests_statuses or {}
+    return task
 
   @staticmethod
   def Get(
       master_name, builder_name, build_number, step_name):  # pragma: no cover
     return WfSwarmingTask._CreateKey(
         master_name, builder_name, build_number, step_name).get()