BigQuery fix for Fuzz Strategy Selection Cron (#723)

* Only upload to bigquery if data is present.

* Added a log message.

src/appengine/handlers/cron/fuzz_strategy_selection.py

@@ -27,6 +27,7 @@
 from google_cloud_utils import big_query
 from handlers import base_handler
 from libs import handler
+from metrics import logs
 
 HIGH_TEMPERATURE_PARAMETER = .75
 MEDIUM_TEMPERATURE_PARAMETER = .5
@@ -176,9 +177,13 @@ def _store_probabilities_in_bigquery(data):
     }
     bigquery_data.append(big_query.Insert(row=bigquery_row, insert_id=None))
 
-  client = big_query.Client(
-      dataset_id='main', table_id='fuzz_strategy_experiments')
-  client.insert(bigquery_data)
+  if bigquery_data:
+    client = big_query.Client(
+        dataset_id='main', table_id='fuzz_strategy_experiments')
+    client.insert(bigquery_data)
+  else:
+    logs.log("No fuzz strategy distribution data was found to upload to "
+             "BigQuery.")
 
 
 def _query_and_upload_strategy_probabilities():