Add default value for HalLink.$source on instantiation

frontend/app/components/api/api-v3/hal-resources/hal-resource.service.test.ts

@@ -46,6 +46,10 @@ describe('HalResource service', () => {
     expect(HalResource).to.exist;
   });
 
+  it('should be instantiable using a default object', () => {
+    expect(new HalResource().href).to.equal(null);
+  });
+
   it('should set its source to _plain if _plain is a property of the source', () => {
     let source = {
       _plain: {

frontend/app/components/api/api-v3/hal-resources/hal-resource.service.ts

@@ -50,7 +50,7 @@ export default class HalResource {
   }
 
   protected static getEmptyResource():any {
-    return {_links: {self: null}};
+    return {_links: {self: {}}};
   }
 
   public get name():string {
@@ -86,7 +86,7 @@ export default class HalResource {
     });
   }
 
-  constructor(public $source:any, public $loaded:boolean = true) {
+  constructor(public $source:any = HalResource.getEmptyResource(), public $loaded:boolean = true) {
     this.$source = $source._plain || $source;
 
     this.proxyProperties();