Qualify the usage of ImmutableMap.of()

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=167723174

javatests/google/registry/flows/domain/DomainTransferRequestFlowTest.java

@@ -320,7 +320,9 @@ public class DomainTransferRequestFlowTest
     // gaining and losing registrars should have a new poll message.
     DomainResource domainAfterAutomaticTransfer = domain.cloneProjectedAtTime(implicitTransferTime);
     // There should be no grace period.
-    assertGracePeriods(domainAfterAutomaticTransfer.getGracePeriods(), ImmutableMap.of());
+    assertGracePeriods(
+        domainAfterAutomaticTransfer.getGracePeriods(),
+        ImmutableMap.<GracePeriod, BillingEvent>of());
   }
 
   private void assertPollMessagesEmitted(