Avoid empty byte array allocations in Proto Lite toByteArray().

In AbstractMessageLite.toByteArray(), check if getSerializedSize() == 0 and return Internal.EMPTY_BYTE_ARRAY directly instead of allocating a new 0-byte array and CodedOutputStream wrappers.

PiperOrigin-RevId: 970010400

java/core/src/main/java/com/google/protobuf/AbstractMessageLite.java

diff --git a/java/core/src/main/java/com/google/protobuf/AbstractMessageLite.java b/java/core/src/main/java/com/google/protobuf/AbstractMessageLite.java
index 884626f..9ca818c 100644
--- a/java/core/src/main/java/com/google/protobuf/AbstractMessageLite.java
+++ b/java/core/src/main/java/com/google/protobuf/AbstractMessageLite.java
@@ -52,7 +52,11 @@
   @Override
   public byte[] toByteArray() {
     try {
-      final byte[] result = new byte[getSerializedSize()];
+      final int size = getSerializedSize();
+      if (size == 0) {
+        return Internal.EMPTY_BYTE_ARRAY;
+      }
+      final byte[] result = new byte[size];
       final CodedOutputStream output = CodedOutputStream.newInstance(result);
       writeTo(output);
       output.checkNoSpaceLeft();