Remove ofy scaffolding from DomainContent and core classes (#1660)

This removes the code that converts between ofy fields and SQL fields in DomainContent and a number of related core classes (basically anything that also needed modification to support the removal from DomainContent).

util/src/main/java/google/registry/util/NullIgnoringCollectionBuilder.java

@@ -0,0 +1,50 @@
+// Copyright 2022 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.util;
+
+import com.google.common.collect.ImmutableCollection;
+import javax.annotation.Nullable;
+
+/**
+ * Collection builder that simply ignores requests to add null elements.
+ *
+ * <p>Useful because we do this in a number of cases.
+ */
+public class NullIgnoringCollectionBuilder<E, B extends ImmutableCollection.Builder<E>> {
+
+  private B builder;
+
+  private NullIgnoringCollectionBuilder(B builder) {
+    this.builder = builder;
+  }
+
+  public static <E2, B2 extends ImmutableCollection.Builder<E2>>
+      NullIgnoringCollectionBuilder<E2, B2> create(B2 builder) {
+    return new NullIgnoringCollectionBuilder<E2, B2>(builder);
+  }
+
+  /** If 'elem' is not null, add it to the builder. */
+  public NullIgnoringCollectionBuilder<E, B> add(@Nullable E elem) {
+    if (elem != null) {
+      builder.add(elem);
+    }
+    return this;
+  }
+
+  /** Returns the underlying builder. */
+  public B getBuilder() {
+    return builder;
+  }
+}

util/src/test/java/google/registry/util/NullIgnoringCollectionBuilderTest.java

@@ -0,0 +1,54 @@
+// Copyright 2022 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.util;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import org.junit.jupiter.api.Test;
+
+public class NullIgnoringCollectionBuilderTest {
+
+  public NullIgnoringCollectionBuilderTest() {}
+
+  @Test
+  public void testNullSafeCollections() {
+    assertThat(
+            NullIgnoringCollectionBuilder.create(new ImmutableList.Builder<Integer>())
+                .getBuilder()
+                .build())
+        .isEqualTo(ImmutableList.of());
+
+    assertThat(
+            NullIgnoringCollectionBuilder.create(new ImmutableList.Builder<Integer>())
+                .add(100)
+                .add(200)
+                .add(null)
+                .getBuilder()
+                .build())
+        .containsExactly(100, 200)
+        .inOrder();
+
+    assertThat(
+            NullIgnoringCollectionBuilder.create(new ImmutableSet.Builder<Integer>())
+                .add(100)
+                .add(200)
+                .add(null)
+                .getBuilder()
+                .build())
+        .containsExactly(100, 200);
+  }
+}