Conform to RDAP Response Profile 15feb19

This is only about the Response Profile, not the Technical Implementation guide.

The Response Profile can be found at https://www.icann.org/en/system/files/files/rdap-response-profile-15feb19-en.pdf

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=250277559

javatests/google/registry/model/domain/DomainBaseTest.java

@@ -207,7 +207,7 @@ public class DomainBaseTest extends EntityTestCase {
                 .isNotNull();
     // This behavior should also hold true for ImmutableObjects nested in collections.
     assertThat(newDomainBase("example.com").asBuilder()
-        .setDsData(ImmutableSet.of(DelegationSignerData.create(1, 1, 1, null)))
+        .setDsData(ImmutableSet.of(DelegationSignerData.create(1, 1, 1, (byte[]) null)))
         .build().getDsData().asList().get(0).getDigest())
             .isNull();
     assertThat(newDomainBase("example.com").asBuilder()