If you are using Lombok, try removing @Data annotation from that class.

In your case from EmployeeDTO. And put @Getter and @Setter annotations after you remove @Data.

Should look like this:

@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor(force = true)
public class EmployeeDTO {

  @Singular
  private final List<PhoneDTO> phones;

}