org.springframework.web.client.RestClientException: Could not extract response: no suitable HttpMessageConverter found for response type [class ru.MyResponse] and content type [application/json;charset=UTF-8]

        
MyRequest request = new MyRequest();
        request.setRequesterId(8);
        MyResponse response = Utils.template().postForObject("url"), request, MyResponse.class);
        response.getResults();

MyResponse{
    private Map<Count, List<SomeClass>> results;

class Utils {
    public static RestTemplate template() {
        RestTemplate template = new RestTemplate();
        List<HttpMessageConverter<?>> converters = new ArrayList<>();
        converters.add(new MappingJackson2HttpMessageConverter());
        converters.add(new StringHttpMessageConverter());
        template.setMessageConverters(converters);
        template.setRequestFactory(new SimpleClientHttpRequestFactory());
        return template;
    }
}

"results":{"ru.Count@6e2fd549":[

public class Count{
   private int count;
   private String name;
   ......
   get/set
}

Map<Count, List<SomeClass>> results;

@Override
        public String toString() {
                return mapper.writeValueAsString(this);
        }

com.fasterxml.jackson.databind.JsonMappingException: Can not find a (Map) Key deserializer

public class TestJson {
    static ObjectMapper mapper = new ObjectMapper();

    public static void main(String[] args) {
        try{
        Map<User, String> map = new HashMap();
        map.put(new User("bla", 1L), "ssss");
        map.put(new User("zzz", 2L), "rrrr");

        Staff staff = new Staff();
        staff.setMyMap(map);

        String jsonString = mapper.writeValueAsString(staff);

        System.out.println("jsonString: " + jsonString);

        Staff obj = mapper.readValue(jsonString, Staff.class);

        System.out.println("Staff: " + obj.getMyMap());

        System.out.println("toObject:" + mapper.writeValueAsString(obj));

        } catch (IOException e) {
            e.printStackTrace();
        }
    }


    static class Staff {
        private Map<User, String> myMap;

        public Staff() {
        }

        public Map<User, String> getMyMap() {
            return myMap;
        }

        public void setMyMap(Map<User, String> myMap) {
            this.myMap = myMap;
        }
    }

    static class User {
        private long id;
        private String name;

        public User(){

        }

        public User(String name, long id) {
            this.name = name;
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public long getId() {
            return id;
        }

        public void setId(long id) {
            this.id = id;
        }

        @Override
        public String toString() {
            try {
                return mapper.writeValueAsString(this);
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }
            return "error";
        }
    }
}

jsonString: {"myMap":{"{\"id\":2,\"name\":\"zzz\"}":"rrrr","{\"id\":1,\"name\":\"bla\"}":"ssss"}}
com.fasterxml.jackson.databind.JsonMappingException: Can not find a (Map) Key deserializer for type [simple type, class ru.test.TestJson$User]

static class User {
        private String name;
        public User(){
        }
        public User(String name) {
            this.name = name;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        @Override
        public String toString() {
            try {
                return mapper.writeValueAsString(this);
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }
            return "error";
        }
    }

jsonString: {"myMap":{"{\"name\":\"bla\"}":"ssss","{\"name\":\"zzz\"}":"rrrr"}}
Staff: {{"name":"{\"name\":\"bla\"}"}=ssss, {"name":"{\"name\":\"zzz\"}"}=rrrr}
toObject:{"myMap":{"{\"name\":\"{\\\"name\\\":\\\"bla\\\"}\"}":"ssss","{\"name\":\"{\\\"name\\\":\\\"zzz\\\"}\"}":"rrrr"}}