Handle nulls better

interop-testing/src/test/java/io/grpc/testing/integration/RetryTest.java

@@ -17,9 +17,8 @@
 package io.grpc.testing.integration;
 
 import static com.google.common.truth.Truth.assertThat;
-import static java.util.concurrent.TimeUnit.NANOSECONDS;
 import static java.util.concurrent.TimeUnit.SECONDS;
-import static junit.framework.TestCase.assertNotNull;
+import static org.junit.Assert.assertNotNull;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.timeout;
@@ -76,6 +75,7 @@
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
+import junit.framework.Assert;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -249,7 +249,8 @@ private void assertRpcStatusRecorded(
     MetricsRecord record = clientStatsRecorder.pollRecord(7, SECONDS);
     assertNotNull(record);
     TagValue statusTag = record.tags.get(RpcMeasureConstants.GRPC_CLIENT_STATUS);
-    assertThat(String.valueOf(statusTag)).isEqualTo(code.toString());
+    Assert.assertNotNull(statusTag);
+    assertThat(statusTag.asString()).isEqualTo(code.toString());
     assertThat(record.getMetricAsLongOrFail(DeprecatedCensusConstants.RPC_CLIENT_FINISHED_COUNT))
         .isEqualTo(1);
     assertThat(record.getMetricAsLongOrFail(RpcMeasureConstants.GRPC_CLIENT_ROUNDTRIP_LATENCY))