title: Could not write JSON: JsonObject; nested exception is com.fasterxml.jackson.databind.JsonMappingException: JsonObject
body: <p>Spring boot 2.5</p>
  
  <pre><code>    @PostMapping("/cart/product")
      public Response addProduct(@RequestBody Map&lt;String, Object&gt; payloadMap) {
          logger.info("addProduct: payloadMap: " + payloadMap);
          String userName = payloadMap.get("user_name").toString();
          final Product product = new ObjectMapper().convertValue(payloadMap.get("product"), Product.class);
          int quantity = (int) payloadMap.get("quantity");
          Cart findCart = cartRepository.findByUsername(userName);
          if (findCart == null) {
              Cart cart = new Cart();
              cart.setCreated(new Date());
              cart.setUsername(userName);
              cart.addProduct(product, quantity);
              cartRepository.save(cart);
              logger.info("addProduct: success_add_product_to_new_cart: " + cart);
              return ResponseService.getSuccessResponse(GsonUtil.gson.toJsonTree(cart));
          } else {
              findCart.addProduct(product, quantity);
              logger.info("addProduct: before_save_exist_cart: " + findCart);
              cartRepository.save(findCart);
              logger.info("addProduct: success_add_product_to_exist_cart: " + findCart);
              return ResponseService.getSuccessResponse(GsonUtil.gson.toJsonTree(findCart));
          }
      }
  
  
  public class ResponseService {
      private static final int SUCCESS_CODE = 0;
      private static final String SUCCESS_MESSAGE = "Success";
      private static final int ERROR_CODE = -1;
  
      private static Logger logger = LogManager.getLogger(ResponseService.class);
  
      public static Response getSuccessResponse(JsonElement body) {
          Response response = new Response(SUCCESS_CODE, SUCCESS_MESSAGE, body);
          logger.info("getSuccessResponse: response = " + response);
          return response;
      }
  
  
  import com.google.gson.JsonElement;
  
  public class Response {
      private int code;
      private String message;
      private JsonElement body;
  
      public Response(int code, String message) {
          this.code = code;
          this.message = message;
      }
  
      public Response(int code, String message, JsonElement body) {
          this.code = code;
          this.message = message;
          this.body = body;
      }
  </code></pre>
  
  <p>But I get error when try to return response:</p>
  
  <pre><code>2020-04-12 12:02:18.825  INFO 9584 --- [nio-8092-exec-1] r.o.s.e.controllers.CartController       : addProduct: success_add_product_to_new_cart: Cart{id=130, username='admin@admin.com', created=Sun Apr 12 12:02:18 EEST 2020, updated=null, productEntities=[
  ProductEntity{id=131, created=Sun Apr 12 12:02:18 EEST 2020, updated=null, quantity=1, orders=null, product=
  Product{id=132, name='product name', description='product description', created=Tue Mar 10 22:34:15 EET 2020, updated=null, price=11.15, currency='EUR', images=[http://www.gravatar.com/avatar/44444?s=200x200&amp;d=identicon, http://www.gravatar.com/avatar/33333?s=200x200&amp;d=identicon]}}], totalAmount=11.15, currency='EUR'}
  2020-04-12 12:02:18.836  INFO 9584 --- [nio-8092-exec-1] r.o.s.e.service.ResponseService          : getSuccessResponse: response = Response{code = 0, message = 'Success', body = '{"id":130,"username":"admin@admin.com","created":"Apr 12, 2020, 12:02:18 PM","productEntities":[{"id":131,"created":"Apr 12, 2020, 12:02:18 PM","quantity":1,"product":{"id":132,"name":"product name","description":"product description","created":"Mar 10, 2020, 10:34:15 PM","price":11.15,"currency":"EUR","images":["http://www.gravatar.com/avatar/44444?s=200x200&amp;d=identicon","http://www.gravatar.com/avatar/33333?s=200x200&amp;d=identicon"]}}],"totalAmount":11.15,"currency":"EUR"}'}
  2020-04-12 12:02:18.861  WARN 9584 --- [nio-8092-exec-1] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: JsonObject; nested exception is com.fasterxml.jackson.databind.JsonMappingException: JsonObject (through reference chain: ru.otus.software_architect.eshop_orders.api.Response["body"]-&gt;com.google.gson.JsonObject["asBoolean"])]
  </code></pre>