Merge pull request #6123 from laravel/note-serializing-value-objects

[7.x] Note about serializing value objects

eloquent-mutators.md

@@ -316,6 +316,8 @@ When casting to value objects, any changes made to the value object will automat
 
     $user->save();
 
+> {tip} If you plan to serialize your Eloquent models containing value objects to JSON or arrays, you should implement the `Illuminate\Contracts\Support\Arrayable` and `JsonSerializable` interfaces on the value object.
+
 #### Inbound Casting
 
 Occasionally, you may need to write a custom cast that only transforms values that are being set on the model and does not perform any operations when attributes are being retrieved from the model. A classic example of an inbound only cast is a "hashing" cast. Inbound only custom casts should implement the `CastsInboundAttributes` interface, which only requires a `set` method to be defined.