Could not extract response: no suitable HttpMessageConverter error in the unit test

Question

I have following code structure : Config.java

public class Config {
  private Map<Context, Set<String>> mapStrings;

  public Map<Context, Set<String>> getMapStrings() {
    return mapStrings;
  }

  public void setMapStrings(Map<Context, Set<String>> mapStrings) {
    this.mapStrings = mapStrings;
  }

  public static class Context {
    private Integer id;
    private String name;

    public Integer getId() {
      return id;
    }

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

    public String getName() {
      return name;
    }

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

controller code :

@RestController("somepath")
@RequestMapping("someMapping")
public class ConfigurationController{

  @GetMapping("")
  public Config get(){
    Config config = new Config();
    return config;
  }
}

Test code :

TestRestTemplate restTemplate
@Test
public void test(){
  String url="url";
  ResponseEntity<Config> response = restTemplate.exchange(
      String.format(url), HttpMethod.GET, null,
      Config.class);
    assertNotNull(response);
}

pom.xml

<dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-annotations</artifactId>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
    </dependency>

Now in spite of having jackson-databind dependency in my pom, I am getting this error :

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

I understand this error is because of the Map that I have used in my config.java. If I convert this map to Map> then it goes away. so for some reason it is not able to convert my custom class Context to json. Can somebody help ? I am using spring-boot. I would preferably like to use some spring/jackson provided http message converter instead of writing my own.