Why does ObjectMapper’s writeValueAsString return an empty string?

I need to serialize Java Object to JSON.

But when I use writeValueAsString method this method returns me empty JSON Object.

Here is my @RestController:

public String getReportsFromReporter(
            @PathVariable(name = "from") String from, 
            @PathVariable(name = "to") String to) throws IOException {
    String url = "example.com";
    ObjectMapper objectMapper = new ObjectMapper();
    ObjectForRequestToReporter objectForRequestToReporter =
                               new ObjectForRequestToReporter();
    objectForRequestToReporter.setToken(somedata);
    objectForRequestToReporter.setEmployee(somedata);
    objectForRequestToReporter.setFrom(from);
    objectForRequestToReporter.setTo(to);
    String jsonObject = objectMapper.writeValueAsString(objectMapper);
    HttpHeaders httpHeaders = new HttpHeaders();
    httpHeaders.setContentType(MediaType.APPLICATION_JSON);
    httpHeaders.setAccept(Collections.singletonList(MediaType.APPLICATION_JSON));
    HttpEntity<String> entity = new HttpEntity<String>(jsonObject, httpHeaders);
    String ans = restTemplate.postForObject(url , entity, String.class);
    String test = objectMapper.writerWithDefaultPrettyPrinter()
                              .writeValueAsString(objectMapper);
    System.out.println(test);
    System.out.println(jsonObject);
    return ans;
}

System.out.println shows this:

 { }
 {}

Gradle depedencies:

implementation("com.fasterxml.jackson.core:jackson-annotations:2.14.2")
implementation("com.fasterxml.jackson.core:jackson-core:2.14.2")
implementation("com.fasterxml.jackson.core:jackson-databind:2.14.2")

Object class for serialize:

@Data
public class ObjectForRequestToReporter {
    private String token;
    private String employee;
    private String from;
    private String to;
    private final int work_after = 0;
}

What am I doing wrong? How can I fix this?