fix for return type issue in 22524

pkg/serialization/lib/serialization.dart

Index: pkg/serialization/lib/serialization.dart
diff --git a/pkg/serialization/lib/serialization.dart b/pkg/serialization/lib/serialization.dart
index e484ae644953b9fb378aacebdec2fedc8c676266..c0ab0d0159d266688053a81aafa8cc97be56b712 100644
--- a/pkg/serialization/lib/serialization.dart
+++ b/pkg/serialization/lib/serialization.dart
@@ -267,7 +267,9 @@ class Serialization {
    * CustomRule subclasses, in which case it requires additional setup and
    * is off by default.
    */
-  void set selfDescribing(bool value) => _selfDescribing = value;
+  void set selfDescribing(bool value) {
+    _selfDescribing = value;
+  }
 
   /**
    * Creates a new serialization with a default set of rules for primitives