Empty Links collection returns null _links

[jasonmitchell]

Expected behaviour is that no "_links" property is included in the response body when a null or empty Links collection is returned from a LinksFor implementation.

For example, given the following method:

public IEnumerable<Link> LinksFor(Person resource)
{
    return new Link[0];
}

The response will include a null "_links" property like below:

{
  "id": 1,
  "firstName": "Geoffrey",
  "lastName": "Merrill",
  "_links": null
}