diff --git a/java/google/registry/flows/domain/DomainAllocateFlow.java b/java/google/registry/flows/domain/DomainAllocateFlow.java
index 413feba5b..54532356e 100644
--- a/java/google/registry/flows/domain/DomainAllocateFlow.java
+++ b/java/google/registry/flows/domain/DomainAllocateFlow.java
@@ -394,7 +394,7 @@ public class DomainAllocateFlow implements TransactionalFlow {
     FeeCreateCommandExtension feeCreate =
         eppInput.getSingleExtension(FeeCreateCommandExtension.class);
     return (feeCreate == null)
-        ? null
+        ? ImmutableList.of()
         : ImmutableList.of(createFeeCreateResponse(feeCreate, commandOperations));
   }
 
diff --git a/java/google/registry/flows/domain/DomainCheckFlow.java b/java/google/registry/flows/domain/DomainCheckFlow.java
index bcfbb83f2..2089805bc 100644
--- a/java/google/registry/flows/domain/DomainCheckFlow.java
+++ b/java/google/registry/flows/domain/DomainCheckFlow.java
@@ -177,7 +177,7 @@ public final class DomainCheckFlow implements Flow {
     FeeCheckCommandExtension<?, ?> feeCheck =
         eppInput.getSingleExtension(FeeCheckCommandExtension.class);
     if (feeCheck == null) {
-      return null;  // No fee checks were requested.
+      return ImmutableList.of();  // No fee checks were requested.
     }
     ImmutableList.Builder<FeeCheckResponseExtensionItem> responseItems =
         new ImmutableList.Builder<>();
diff --git a/java/google/registry/flows/domain/DomainCreateFlow.java b/java/google/registry/flows/domain/DomainCreateFlow.java
index 520e38fc7..a2da29949 100644
--- a/java/google/registry/flows/domain/DomainCreateFlow.java
+++ b/java/google/registry/flows/domain/DomainCreateFlow.java
@@ -439,7 +439,7 @@ public class DomainCreateFlow implements TransactionalFlow {
   private ImmutableList<FeeTransformResponseExtension> createResponseExtensions(
       FeeCreateCommandExtension feeCreate, EppCommandOperations commandOperations) {
     return (feeCreate == null)
-        ? null
+        ? ImmutableList.of()
         : ImmutableList.of(createFeeCreateResponse(feeCreate, commandOperations));
   }
 
diff --git a/java/google/registry/flows/domain/DomainDeleteFlow.java b/java/google/registry/flows/domain/DomainDeleteFlow.java
index e1d08d1a8..055aa4cdb 100644
--- a/java/google/registry/flows/domain/DomainDeleteFlow.java
+++ b/java/google/registry/flows/domain/DomainDeleteFlow.java
@@ -221,7 +221,7 @@ public final class DomainDeleteFlow implements TransactionalFlow {
       DomainResource existingDomain, DateTime now) {
     FeeTransformResponseExtension.Builder feeResponseBuilder = getDeleteResponseBuilder();
     if (feeResponseBuilder == null) {
-      return null;
+      return ImmutableList.of();
     }
     ImmutableList.Builder<Credit> creditsBuilder = new ImmutableList.Builder<>();
     for (GracePeriod gracePeriod : existingDomain.getGracePeriods()) {
@@ -234,7 +234,7 @@ public final class DomainDeleteFlow implements TransactionalFlow {
     }
     ImmutableList<Credit> credits = creditsBuilder.build();
     if (credits.isEmpty()) {
-      return null;
+      return ImmutableList.of();
     }
     return ImmutableList.of(feeResponseBuilder.setCredits(credits).build());
   }
diff --git a/java/google/registry/flows/domain/DomainInfoFlow.java b/java/google/registry/flows/domain/DomainInfoFlow.java
index 5d0b1a353..447fb9eab 100644
--- a/java/google/registry/flows/domain/DomainInfoFlow.java
+++ b/java/google/registry/flows/domain/DomainInfoFlow.java
@@ -19,7 +19,6 @@ import static google.registry.flows.ResourceFlowUtils.loadAndVerifyExistence;
 import static google.registry.flows.ResourceFlowUtils.verifyOptionalAuthInfo;
 import static google.registry.flows.domain.DomainFlowUtils.addSecDnsExtensionIfPresent;
 import static google.registry.flows.domain.DomainFlowUtils.handleFeeRequest;
-import static google.registry.util.CollectionUtils.forceEmptyToNull;
 
 import com.google.common.base.Optional;
 import com.google.common.collect.ImmutableList;
@@ -149,6 +148,6 @@ public final class DomainInfoFlow implements Flow {
         extensions.add(FlagsInfoResponseExtension.create(ImmutableList.copyOf(flags)));
       }
     }
-    return forceEmptyToNull(extensions.build());
+    return extensions.build();
   }
 }
diff --git a/java/google/registry/flows/domain/DomainRenewFlow.java b/java/google/registry/flows/domain/DomainRenewFlow.java
index a9a5f8a5a..f6af5a3c9 100644
--- a/java/google/registry/flows/domain/DomainRenewFlow.java
+++ b/java/google/registry/flows/domain/DomainRenewFlow.java
@@ -216,11 +216,12 @@ public final class DomainRenewFlow implements TransactionalFlow {
 
   private ImmutableList<FeeTransformResponseExtension> createResponseExtensions(
       Money renewCost, FeeRenewCommandExtension feeRenew) {
-    return (feeRenew == null) ? null : ImmutableList.of(feeRenew
-        .createResponseBuilder()
-        .setCurrency(renewCost.getCurrencyUnit())
-        .setFees(ImmutableList.of(Fee.create(renewCost.getAmount(), FeeType.RENEW)))
-        .build());
+    return (feeRenew == null)
+        ? ImmutableList.of()
+        : ImmutableList.of(feeRenew.createResponseBuilder()
+            .setCurrency(renewCost.getCurrencyUnit())
+            .setFees(ImmutableList.of(Fee.create(renewCost.getAmount(), FeeType.RENEW)))
+            .build());
   }
 
   /** The domain has a pending transfer on it and so can't be explicitly renewed. */
diff --git a/java/google/registry/flows/domain/DomainRestoreRequestFlow.java b/java/google/registry/flows/domain/DomainRestoreRequestFlow.java
index 94a1958b3..8beaa5ef8 100644
--- a/java/google/registry/flows/domain/DomainRestoreRequestFlow.java
+++ b/java/google/registry/flows/domain/DomainRestoreRequestFlow.java
@@ -260,8 +260,9 @@ public final class DomainRestoreRequestFlow implements TransactionalFlow  {
 
   private static ImmutableList<FeeTransformResponseExtension> createResponseExtensions(
       Money restoreCost, Money renewCost, FeeUpdateCommandExtension feeUpdate) {
-    return (feeUpdate == null) ? null : ImmutableList.of(
-        feeUpdate.createResponseBuilder()
+    return (feeUpdate == null)
+        ? ImmutableList.of()
+        : ImmutableList.of(feeUpdate.createResponseBuilder()
             .setCurrency(restoreCost.getCurrencyUnit())
             .setFees(ImmutableList.of(
                 Fee.create(restoreCost.getAmount(), FeeType.RESTORE),
diff --git a/java/google/registry/flows/domain/DomainTransferRequestFlow.java b/java/google/registry/flows/domain/DomainTransferRequestFlow.java
index 6c0c2d9cd..053783365 100644
--- a/java/google/registry/flows/domain/DomainTransferRequestFlow.java
+++ b/java/google/registry/flows/domain/DomainTransferRequestFlow.java
@@ -408,7 +408,7 @@ public final class DomainTransferRequestFlow implements TransactionalFlow {
   private ImmutableList<FeeTransformResponseExtension> createResponseExtensions(Money renewCost,
       FeeTransferCommandExtension feeTransfer) {
     return feeTransfer == null
-        ? null
+        ? ImmutableList.of()
         : ImmutableList.of(feeTransfer.createResponseBuilder()
             .setCurrency(renewCost.getCurrencyUnit())
             .setFees(ImmutableList.of(Fee.create(renewCost.getAmount(), FeeType.RENEW)))
diff --git a/java/google/registry/flows/poll/PollRequestFlow.java b/java/google/registry/flows/poll/PollRequestFlow.java
index 822b20e38..af4bca6a5 100644
--- a/java/google/registry/flows/poll/PollRequestFlow.java
+++ b/java/google/registry/flows/poll/PollRequestFlow.java
@@ -18,7 +18,6 @@ import static google.registry.flows.FlowUtils.validateClientIsLoggedIn;
 import static google.registry.flows.poll.PollFlowUtils.getPollMessagesQuery;
 import static google.registry.model.eppoutput.Result.Code.SUCCESS_WITH_ACK_MESSAGE;
 import static google.registry.model.eppoutput.Result.Code.SUCCESS_WITH_NO_MESSAGES;
-import static google.registry.util.CollectionUtils.forceEmptyToNull;
 
 import com.googlecode.objectify.Key;
 import google.registry.flows.EppException;
@@ -76,8 +75,8 @@ public class PollRequestFlow implements Flow {
             .setQueueLength(getPollMessagesQuery(clientId, now).count())
             .setMessageId(PollMessage.EXTERNAL_KEY_CONVERTER.convert(Key.create(pollMessage)))
             .build())
-        .setMultipleResData(forceEmptyToNull(pollMessage.getResponseData()))
-        .setExtensions(forceEmptyToNull(pollMessage.getResponseExtensions()))
+        .setMultipleResData(pollMessage.getResponseData())
+        .setExtensions(pollMessage.getResponseExtensions())
         .build();
   }
 
diff --git a/java/google/registry/model/eppoutput/EppResponse.java b/java/google/registry/model/eppoutput/EppResponse.java
index 49352ba89..736e47396 100644
--- a/java/google/registry/model/eppoutput/EppResponse.java
+++ b/java/google/registry/model/eppoutput/EppResponse.java
@@ -14,6 +14,9 @@
 
 package google.registry.model.eppoutput;
 
+import static google.registry.util.CollectionUtils.forceEmptyToNull;
+import static google.registry.util.CollectionUtils.nullToEmptyImmutableCopy;
+
 import com.google.common.collect.FluentIterable;
 import com.google.common.collect.ImmutableList;
 import google.registry.model.Buildable;
@@ -150,11 +153,11 @@ public class EppResponse extends ImmutableObject implements ResponseOrGreeting {
   ImmutableList<? extends ResponseExtension> extensions;
 
   public ImmutableList<? extends ResponseData> getResponseData() {
-    return resData;
+    return nullToEmptyImmutableCopy(resData);
   }
 
   public ImmutableList<? extends ResponseExtension> getExtensions() {
-    return extensions;
+    return nullToEmptyImmutableCopy(extensions);
   }
 
   @Nullable
@@ -216,8 +219,8 @@ public class EppResponse extends ImmutableObject implements ResponseOrGreeting {
       return setMultipleResData(ImmutableList.of(onlyResData));
     }
 
-    public Builder setMultipleResData(@Nullable ImmutableList<? extends ResponseData> resData) {
-      getInstance().resData = resData;
+    public Builder setMultipleResData(ImmutableList<? extends ResponseData> resData) {
+      getInstance().resData = forceEmptyToNull(resData);
       return this;
     }
 
@@ -225,8 +228,8 @@ public class EppResponse extends ImmutableObject implements ResponseOrGreeting {
       return setExtensions(ImmutableList.of(onlyExtension));
     }
 
-    public Builder setExtensions(@Nullable ImmutableList<? extends ResponseExtension> extensions) {
-      getInstance().extensions = extensions;
+    public Builder setExtensions(ImmutableList<? extends ResponseExtension> extensions) {
+      getInstance().extensions = forceEmptyToNull(extensions);
       return this;
     }
   }