JAXB error when trying to create a list of elements

I am trying to support the hypermedia constraint using link elements as per http://ift.tt/KQfcf6 in my response XML. I have a BankAccount object and I can return one link element on its own but I am having trouble when trying to return a list of link elements (even one on its own in a list is an issue). I would prefer not to have to encapsulate the link elements in a links parent element; I would prefer to list off the link elements.

My BankAccount class is as follows:

@XmlRootElement(name = "bankaccount")
@XmlType(propOrder={"branchCode","accountNo","custName", "custAddress", "custType", "custRating", "balance", "link"})

public class BankAccount {
    private String branchCode, accountNo, custName, custAddress, custType, custRating;
    private double balance;
//    private Link link = new Link();   // works
    private List<Link> links;// = new ArrayList<>();

    public BankAccount(){

    }
    public BankAccount(String branchCode, String accountNo, String custName, String custAddress, String custType, String custRating, double balance) {
        this.branchCode = branchCode;
        this.accountNo = accountNo;
        this.custName = custName;
        this.custAddress = custAddress;
        this.custType = custType;
        this.custRating = custRating;
        this.balance = balance;
    }

    @XmlElement
    public void setBranchCode(String branchCode) {
        this.branchCode = branchCode;
    }
    public String getBranchCode() {
        return branchCode;
    }
    // other setters and getters...

    // the link element on its own that works...
    //    @XmlElement(name = "link")
    //    public void setLink(Link aLink){
    //        this.link = aLink;
    //    }
    //    public Link getLink(){
    //        return link;
    //    }

    @XmlElement(name = "link")
    public List<Link> getLinks() {
        return links;
    }

    public void setLinks(List<Link> links) {
        this.links = links;
    }
}

The Link class:

@XmlAccessorType(XmlAccessType.FIELD)   
public class Link {
   @XmlAttribute(name = "rel")
   private String rel;

   @XmlAttribute(name = "href")
   private String href;

   public String getRel() {
      return rel;
   }
   public void setRel(String aRel){
      this.rel = aRel;
   }

   public String getHref() {
      return href;
   }
   public void setHref(String href){
      this.href = href;
   }

}

Lastly, my RESTful WS code:

        // hypermedia constraint...
        bankAccount.setLinks(new ArrayList<Link>());

        Link linkSelf = new Link();
        linkSelf.setRel("self");
        linkSelf.setHref("/"+bankNSC+"/"+bankAccountNumber);

        bankAccount.getLinks().add(linkSelf);
        return Response.status(Response.Status.OK).entity(bankAccount).build();

I am getting a status 500 error :

The server encountered an internal error that prevented it from fulfilling this request

Any help very much appreciated...

Thanks, Sean.