Support for empty arrays in the embedded representations

[slayful]

As far as I've checked it's not possible to add a sub representation which will yield an empty array in the "_embedded" field.

I've modified the repositories to enable this.

Trying to serialise this representation:

    String href = "customer/123456";
    ReadableRepresentation party = newBaseResource(href)
                                       .withLink("ns:users", BASE_URL + href + "?users")
                                       .withRepresentation("ns:users",  representationFactory
                                           .newRepresentation("1")
                                           .setEmptySubRepresentation(true));

will yield the following JSON:

{
  "_links" : {
    "curies" : [ {
      "href" : "https://example.com/apidocs/ns/{rel}",
      "name" : "ns",
      "templated" : true
    }, {
      "href" : "https://example.com/apidocs/role/{rel}",
      "name" : "role",
      "templated" : true
    } ],
    "self" : {
      "href" : "https://example.com/api/customer/123456"
    },
    "ns:parent" : {
      "href" : "https://example.com/api/customer/1234",
      "name" : "bob",
      "title" : "The Parent",
      "hreflang" : "en"
    },
    "ns:users" : {
      "href" : "https://example.com/api/customer/123456?users"
    }
  },
  "_embedded" : {
    "ns:users" : [ ]
  }
}

[slayful]

The list of pull requests:
HalBuilder/halbuilder-api#11
HalBuilder/halbuilder-test-resources#9
HalBuilder/halbuilder-core#32
#17

[talios]

What's the use case for this? I'm wondering in what scenario you would would to ever have an empty array? I assume you have client consumption code that's treating the serialized JSON as plain JSON and doesn't want to handle any null checks.

I see the halbuilder-core PR is against the develop branch, which is an API breaking in-progress branch that doesn't work with halbuilder-json - so as it is these couldn't work together anyway.

Under the new API rel's are promoted to being a first class construct ( singletons, arrays ) and might serve to allow this in a cleaner manner.