1 files changed, 7 insertions, 1 deletions
diff --git a/api/src/main/java/io/opencensus/metrics/export/Metric.java b/api/src/main/java/io/opencensus/metrics/export/Metric.java
index 07fe356a..5e2fa5e8 100644
--- a/api/src/main/java/io/opencensus/metrics/export/Metric.java
+++ b/api/src/main/java/io/opencensus/metrics/export/Metric.java
@@ -23,6 +23,8 @@ import io.opencensus.metrics.export.Value.ValueDistribution;
 import io.opencensus.metrics.export.Value.ValueDouble;
 import io.opencensus.metrics.export.Value.ValueLong;
 import io.opencensus.metrics.export.Value.ValueSummary;
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import javax.annotation.concurrent.Immutable;
 
@@ -47,8 +49,12 @@ public abstract class Metric {
    * @since 0.17
    */
   public static Metric create(MetricDescriptor metricDescriptor, List<TimeSeries> timeSeriesList) {
+    Utils.checkNotNull(metricDescriptor, "metricDescriptor");
+    Utils.checkNotNull(timeSeriesList, "timeSeriesList");
+    Utils.checkListElementNotNull(timeSeriesList, "timeSeries");
     checkTypeMatch(metricDescriptor.getType(), timeSeriesList);
-    return new AutoValue_Metric(metricDescriptor, timeSeriesList);
+    return new AutoValue_Metric(
+        metricDescriptor, Collections.unmodifiableList(new ArrayList<TimeSeries>(timeSeriesList)));
   }
 
   /**