Merge from google internal

2 files changed, 12 insertions, 2 deletions

diff --git a/java/util/src/main/java/com/google/protobuf/util/FieldMaskTree.java b/java/util/src/main/java/com/google/protobuf/util/FieldMaskTree.java
index b192b53e..e017b987 100644
--- a/java/util/src/main/java/com/google/protobuf/util/FieldMaskTree.java
+++ b/java/util/src/main/java/com/google/protobuf/util/FieldMaskTree.java
@@ -34,7 +34,6 @@ import com.google.protobuf.Descriptors.Descriptor;
 import com.google.protobuf.Descriptors.FieldDescriptor;
 import com.google.protobuf.FieldMask;
 import com.google.protobuf.Message;
-
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map.Entry;
@@ -244,6 +243,11 @@ final class FieldMaskTree {
                   + "singluar message field and cannot have sub-fields.");
           continue;
         }
+        if (!source.hasField(field) && !destination.hasField(field)) {
+          // If the message field is not present in both source and destination, skip recursing
+          // so we don't create unneccessary empty messages.
+          continue;
+        }
         String childPath = path.isEmpty() ? entry.getKey() : path + "." + entry.getKey();
         merge(
             entry.getValue(),
diff --git a/java/util/src/test/java/com/google/protobuf/util/FieldMaskTreeTest.java b/java/util/src/test/java/com/google/protobuf/util/FieldMaskTreeTest.java
index 3ee0fc6e..853b6151 100644
--- a/java/util/src/test/java/com/google/protobuf/util/FieldMaskTreeTest.java
+++ b/java/util/src/test/java/com/google/protobuf/util/FieldMaskTreeTest.java
@@ -33,7 +33,6 @@ package com.google.protobuf.util;
 import protobuf_unittest.UnittestProto.NestedTestAllTypes;
 import protobuf_unittest.UnittestProto.TestAllTypes;
 import protobuf_unittest.UnittestProto.TestAllTypes.NestedMessage;
-
 import junit.framework.TestCase;
 
 public class FieldMaskTreeTest extends TestCase {
@@ -222,6 +221,13 @@ public class FieldMaskTreeTest extends TestCase {
     new FieldMaskTree().addFieldPath("payload").merge(clearedSource, builder, options);
     assertEquals(false, builder.hasPayload());
 
+    // Skip a message field if they are unset in both source and target.
+    builder = NestedTestAllTypes.newBuilder();
+    new FieldMaskTree()
+        .addFieldPath("payload.optional_int32")
+        .merge(clearedSource, builder, options);
+    assertEquals(false, builder.hasPayload());
+
     // Change to replace message fields.
     options.setReplaceMessageFields(true);
     builder = NestedTestAllTypes.newBuilder();