Use jsonSerialize in StateCaster

src/StateCaster.php

@@ -81,7 +81,7 @@ public function set($model, string $key, $value, array $attributes): ?string
      */
     public function serialize($model, string $key, $value, array $attributes)
     {
-        return $value instanceof State ? $value->getValue() : $value;
+        return $value instanceof State ? $value->jsonSerialize() : $value;
     }
 
     private function getStateMapping(): Collection

tests/Dummy/ModelStates/StateB.php

@@ -4,4 +4,8 @@
 
 class StateB extends ModelState
 {
+    public function jsonSerialize()
+    {
+        return ['name' => 'StateB'];
+    }
 }

tests/StateCastingTest.php

@@ -137,8 +137,16 @@ public function registerStates(): void
     expect($model->state->getField())->toEqual('state');
 });
 
-it('serializes to a value', function() {
+it('serializes to a value when calling toArray', function() {
     $model = new TestModel();
 
     expect($model->toArray()['state'])->toBe(StateA::class);
 });
+
+it('respects jsonSerialize in state classes', function() {
+    $model = new TestModel([
+        'state' => StateB::class,
+    ]);
+
+    expect($model->toJson())->toBe('{"state":{"name":"StateB"}}');
+});