Handle nullness properly in some message/flow/poll code

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=127543268

java/google/registry/flows/Flow.java

@@ -27,6 +27,7 @@ import google.registry.model.eppoutput.Result;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
+import javax.annotation.Nullable;
 import org.joda.time.DateTime;
 
 /**
@@ -78,8 +79,8 @@ public abstract class Flow {
 
   protected EppOutput createOutput(
       Result.Code code,
-      ResponseData responseData,
-      ImmutableList<? extends ResponseExtension> extensions) {
+      @Nullable ResponseData responseData,
+      @Nullable ImmutableList<? extends ResponseExtension> extensions) {
     return EppOutput.create(new EppResponse.Builder()
         .setTrid(trid)
         .setResult(Result.create(code))

java/google/registry/flows/ResourceDeleteFlow.java

@@ -25,6 +25,7 @@ import google.registry.model.eppoutput.EppOutput;
 import google.registry.model.eppoutput.EppResponse.ResponseExtension;
 import google.registry.model.eppoutput.Result.Code;
 import java.util.Set;
+import javax.annotation.Nullable;
 
 /**
  * An EPP flow that deletes an {@link EppResource}.
@@ -58,6 +59,7 @@ public abstract class ResourceDeleteFlow<R extends EppResource, C extends Single
   }
 
   /** Subclasses can override this to return response extensions. */
+  @Nullable
   protected ImmutableList<? extends ResponseExtension> getDeleteResponseExtensions() {
     return null;
   }

java/google/registry/flows/poll/PollFlow.java

@@ -31,6 +31,7 @@ import google.registry.model.eppoutput.Result;
 import google.registry.model.poll.MessageQueueInfo;
 import google.registry.model.poll.PollMessage;
 import java.util.List;
+import javax.annotation.Nullable;
 
 /** Base class of EPP Poll command flows. Mostly provides datastore helper methods. */
 public abstract class PollFlow extends LoggedInFlow {
@@ -74,8 +75,8 @@ public abstract class PollFlow extends LoggedInFlow {
   protected EppOutput createOutput(
       Result.Code code,
       MessageQueueInfo messageQueueInfo,
-      ImmutableList<ResponseData> responseData,
-      ImmutableList<ResponseExtension> responseExtensions) {
+      @Nullable ImmutableList<ResponseData> responseData,
+      @Nullable ImmutableList<ResponseExtension> responseExtensions) {
     return EppOutput.create(new EppResponse.Builder()
         .setTrid(trid)
         .setResult(Result.create(code))

java/google/registry/model/eppoutput/EppResponse.java

@@ -47,6 +47,7 @@ import google.registry.model.poll.PendingActionNotificationResponse.ContactPendi
 import google.registry.model.poll.PendingActionNotificationResponse.DomainPendingActionNotificationResponse;
 import google.registry.model.transfer.TransferResponse.ContactTransferResponse;
 import google.registry.model.transfer.TransferResponse.DomainTransferResponse;
+import javax.annotation.Nullable;
 import javax.xml.bind.annotation.XmlElement;
 import javax.xml.bind.annotation.XmlElementRef;
 import javax.xml.bind.annotation.XmlElementRefs;
@@ -187,12 +188,12 @@ public class EppResponse extends ImmutableObject implements ResponseOrGreeting {
       return this;
     }
 
-    public Builder setResData(ImmutableList<? extends ResponseData> resData) {
+    public Builder setResData(@Nullable ImmutableList<? extends ResponseData> resData) {
       getInstance().resData = resData;
       return this;
     }
 
-    public Builder setExtensions(ImmutableList<? extends ResponseExtension> extensions) {
+    public Builder setExtensions(@Nullable ImmutableList<? extends ResponseExtension> extensions) {
       getInstance().extensions = extensions;
       return this;
     }

java/google/registry/model/poll/MessageQueueInfo.java

@@ -14,7 +14,10 @@
 
 package google.registry.model.poll;
 
+import static com.google.common.base.Preconditions.checkNotNull;
+
 import google.registry.model.ImmutableObject;
+import javax.annotation.Nullable;
 import javax.xml.bind.annotation.XmlAttribute;
 import javax.xml.bind.annotation.XmlElement;
 import org.joda.time.DateTime;
@@ -54,15 +57,15 @@ public class MessageQueueInfo extends ImmutableObject {
   }
 
   public static MessageQueueInfo create(
-      DateTime queueDate,
-      String msg,
+      @Nullable DateTime queueDate,
+      @Nullable String msg,
       Integer queueLength,
       String messageId) {
     MessageQueueInfo instance = new MessageQueueInfo();
     instance.queueDate = queueDate;
     instance.msg = msg;
-    instance.queueLength = queueLength;
-    instance.messageId = messageId;
+    instance.queueLength = checkNotNull(queueLength);
+    instance.messageId = checkNotNull(messageId);
     return instance;
   }
 }