fix empty message serialization for Any

php/src/Google/Protobuf/Internal/Message.php

@@ -1980,8 +1980,12 @@ class Message
                 $size += 9;
                 $size += $value_msg->jsonByteSize();
             } else {
-                // Size for value. +1 for comma, -2 for "{}".
-                $size += $value_msg->jsonByteSize() -1;
+                $value_size = $value_msg->jsonByteSize();
+                // size === 2 it's empty message {} which is not serialized inside any
+                if ($value_size !== 2) {
+                    // Size for value. +1 for comma, -2 for "{}".
+                    $size += $value_size -1;
+                }
             }
         } elseif (get_class($this) === 'Google\Protobuf\FieldMask') {
             $field_mask = GPBUtil::formatFieldMask($this);

php/tests/EncodeDecodeTest.php

@@ -5,6 +5,7 @@ require_once('test_util.php');
 
 use Google\Protobuf\RepeatedField;
 use Google\Protobuf\GPBType;
+use Foo\EmptyAnySerialization;
 use Foo\TestInt32Value;
 use Foo\TestInt64Value;
 use Foo\TestUInt32Value;
@@ -1513,4 +1514,22 @@ class EncodeDecodeTest extends TestBase
             [TestStringValue::class, "a", "\"a\"", "", "\"\""],
         ];
     }
+
+    public function testEmptyAnySerialization()
+    {
+        $m = new EmptyAnySerialization();
+
+        $any = new Any();
+        $any->pack($m);
+
+        $data = $any->serializeToJsonString();
+        $this->assertEquals('{"@type":"type.googleapis.com/foo.EmptyAnySerialization"}', $data);
+
+        $any = new Any();
+        $any->mergeFromJsonString($data);
+
+        $m = $any->unpack();
+        $this->assertInstanceOf(EmptyAnySerialization::class, $m);
+        $this->assertEquals('', $m->getA());
+    }
 }

php/tests/proto/test.proto

@@ -168,6 +168,10 @@ message ARRAY {
   int32 a = 1;
 }
 
+message EmptyAnySerialization {
+  string a = 1;
+}
+
 message TestPackedMessage {
   repeated int32    repeated_int32    = 90  [packed = true];
   repeated int64    repeated_int64    = 91  [packed = true];