Sorry, I've forgotten, here is how my DTO looks like:

public class EmployersPracticesDTO implements Serializable {

     /**
      * needed during serialization
      */
     private static final long serialVersionUID = -1674163395194600978L;
     
     private List<EmployerOfferedPractices> employerOfferedPractices;
     
     public EmployersPracticesDTO() {
          this.employerOfferedPractices = 
               new ArrayList<EmployerOfferedPractices>();
     }
     
     public void addEmployerOfferedPractices(
               EmployerOfferedPractices employerOfferedPractices) {
          this.employerOfferedPractices.add(employerOfferedPractices);
     }

     public List<EmployerOfferedPractices> getEmployerOfferedPractices() {
          return employerOfferedPractices;
     }

     public static class EmployerOfferedPractices implements Serializable {
          /**
           * needed during serialization
           */
          private static final long serialVersionUID = 7578584034230432388L;
          
          private String companyName;
          private int numberOfDonePractices;

          public EmployerOfferedPractices(String companyName, int numberOfPractices) {
               this.companyName = companyName;
               this.numberOfDonePractices = numberOfPractices;
          }

          public int getNumberOfPracticesDone() {
               return numberOfDonePractices;
          }

          
          public String getCompanyName() {
               return companyName;
          }
     }
}