Fix MetricActivationsTest

Bug: 196750069

Test: atest CtsStatsdHostTestCases
Change-Id: I0e0299d684ace4238d23a00010f41ac4bd4ea972
diff --git a/tests/src/android/cts/statsd/atom/AtomTestCase.java b/tests/src/android/cts/statsd/atom/AtomTestCase.java
index 14c3072..f0324c0 100644
--- a/tests/src/android/cts/statsd/atom/AtomTestCase.java
+++ b/tests/src/android/cts/statsd/atom/AtomTestCase.java
@@ -1225,7 +1225,7 @@
     protected List<EventMetricData> backfillAggregatedAtomsInEventMetric(
             EventMetricData metricData) {
       if (!metricData.hasAggregatedAtomInfo()) {
-        return Collections.emptyList();
+        return Collections.singletonList(metricData);
       }
       List<EventMetricData> data = new ArrayList<>();
       StatsLog.AggregatedAtomInfo atomInfo = metricData.getAggregatedAtomInfo();