Handle when there are no dashboard for service_id

This is tested by adding a data point to the fixture for which the
service_id matched no dashboard config in our test. As a result we
return an empty array. Without this code change an exception was thrown
as the list index was out of range.

backdrop/transformers/tasks/latest_transaction_explorer_values.py

@@ -61,9 +61,9 @@ def _service_ids_with_latest_data(data):
 
 def _dashboard_configs_with_latest_data(data):
     for service_id, latest_data in _service_ids_with_latest_data(data):
-        dashboard_config = admin_api.get_dashboard_by_tx_id(service_id)[0]
-        if dashboard_config:
-            yield dashboard_config, latest_data
+        dashboard_configs = admin_api.get_dashboard_by_tx_id(service_id)
+        if dashboard_configs:
+            yield dashboard_configs[0], latest_data
 
 
 def _get_data_points_for_each_tx_metric(data, transform, data_set_config):

tests/transformers/fixtures/transactions_explorer_example_data.json

@@ -78,5 +78,25 @@
         "service_id": "sorn-innit",
         "total_cost": 6203480.9399999995,
         "type": "seasonally-adjusted"
+    },
+    {
+        "_day_start_at": "2012-01-01T00:00:00+00:00",
+        "_hour_start_at": "2012-01-01T00:00:00+00:00",
+        "_id": "MjAxMi0wMS0wMSAwMDowMDowMDIwMTMtMDEtMDEgMDA6MDA6MDBiaXMtYW5udWFsLXJldHVybnM=",
+        "_month_start_at": "2012-01-01T00:00:00+00:00",
+        "_quarter_start_at": "2012-01-01T00:00:00+00:00",
+        "_timestamp": "2012-01-01T00:00:00+00:00",
+        "_updated_at": "2014-03-19T10:44:32.287000+00:00",
+        "_week_start_at": "2013-12-26T00:00:00+00:00",
+        "cost_per_transaction": 2.63,
+        "digital_cost_per_transaction": 2.36,
+        "digital_takeup": 0.9756123825537215,
+        "end_at": "2013-01-01T00:00:00+00:00",
+        "number_of_digital_transactions": 2301214,
+        "number_of_transactions": 2358738,
+        "period": "year",
+        "service_id": "something-without-a-dashboard",
+        "total_cost": 6203480.9399999995,
+        "type": "seasonally-adjusted"
     }
 ]