[Findit] Fix bugs when pulling gtest result.

appengine/findit/waterfall/swarming_util.py

Index: appengine/findit/waterfall/swarming_util.py
diff --git a/appengine/findit/waterfall/swarming_util.py b/appengine/findit/waterfall/swarming_util.py
index 9f9a9fde95f4fcc673705bd1235ce4ec92daead6..20a1918741c793fb4665a2bae6a65a4a3a792289 100644
--- a/appengine/findit/waterfall/swarming_util.py
+++ b/appengine/findit/waterfall/swarming_util.py
@@ -48,6 +48,10 @@ URLFETCH_CONNECTION_CLOSED_ERROR = 120
 EXCEEDED_MAX_RETRIES_ERROR = 210
 
 
+# Outputs_ref is None.
+NO_TASK_OUTPUTS = 300
+
+
 # Other/miscellaneous error codes.
 UNKNOWN = 1000
 
@@ -269,7 +273,7 @@ def GetIsolatedDataForFailedBuild(
       # Only retrieves test results from tasks which have failures and
       # the failure should not be internal infrastructure failure.
       swarming_step_name = GetTagValue(item['tags'], tag_name)
-      if swarming_step_name in failed_steps:
+      if swarming_step_name in failed_steps and item.get('outputs_ref'):
         isolated_data = _GenerateIsolatedData(item['outputs_ref'])
         build_isolated_data[swarming_step_name].append(isolated_data)