fix(renderer): handle empty fragments correctly

Closes angular#3100

Author: tbosch

modules/angular2/src/render/dom/dom_renderer.ts

@@ -83,8 +83,10 @@ export class DomRenderer extends Renderer {
   attachFragmentAfterFragment(previousFragmentRef: RenderFragmentRef,
                               fragmentRef: RenderFragmentRef) {
     var previousFragmentNodes = resolveInternalDomFragment(previousFragmentRef);
-    var sibling = previousFragmentNodes[previousFragmentNodes.length - 1];
-    moveNodesAfterSibling(sibling, resolveInternalDomFragment(fragmentRef));
+    if (previousFragmentNodes.length > 0) {
+      var sibling = previousFragmentNodes[previousFragmentNodes.length - 1];
+      moveNodesAfterSibling(sibling, resolveInternalDomFragment(fragmentRef));
+    }
   }
 
   attachFragmentAfterElement(elementRef: RenderElementRef, fragmentRef: RenderFragmentRef) {
@@ -253,7 +255,7 @@ export class DomRenderer extends Renderer {
 }
 
 function moveNodesAfterSibling(sibling, nodes) {
-  if (isPresent(DOM.parentElement(sibling))) {
+  if (nodes.length > 0 && isPresent(DOM.parentElement(sibling))) {
     for (var i = 0; i < nodes.length; i++) {
       DOM.insertBefore(sibling, nodes[i]);
     }

modules/angular2/test/render/dom/dom_renderer_integration_spec.ts

@@ -197,6 +197,33 @@ export function main() {
              });
        }));
 
+    it('should add and remove empty fragments',
+       inject([AsyncTestCompleter, DomTestbed], (async, tb: DomTestbed) => {
+         tb.compileAndMerge(someComponent,
+                            [
+                              new ViewDefinition({
+                                componentId: 'someComponent',
+                                template: '<template></template><template></template>',
+                                directives: []
+                              })
+                            ])
+             .then((protoViewMergeMappings) => {
+               var rootView = tb.createView(protoViewMergeMappings[0]);
+
+               var elr = elRef(rootView.viewRef, 1);
+               expect(rootView.hostElement).toHaveText('');
+               var fragment = rootView.fragments[1];
+               var fragment2 = rootView.fragments[2];
+               tb.renderer.attachFragmentAfterElement(elr, fragment);
+               tb.renderer.attachFragmentAfterFragment(fragment, fragment2);
+               tb.renderer.detachFragment(fragment);
+               tb.renderer.detachFragment(fragment2);
+               expect(rootView.hostElement).toHaveText('');
+
+               async.done();
+             });
+       }));
+
     it('should handle events', inject([AsyncTestCompleter, DomTestbed], (async, tb: DomTestbed) => {
          tb.compileAndMerge(someComponent,
                             [