fix: no elements in sequence error (#1029)

Sometimes this error is appearing `EmptyError: no elements in sequence`, add `defaultIfEmpty` so that it can complete

Author: alan-agius4

integration/watch/basic.spec.ts

@@ -53,6 +53,14 @@ describe('basic', () => {
           expect(error.message).to.match(/is not assignable to type 'boolean'/);
         });
       });
+
+      it('should emit complete when a file changes outside of the compilation', done => {
+        harness.copyTestCase('new-file');
+
+        harness.onComplete(() => {
+          done();
+        });
+      });
     });
   });
 

integration/watch/basic/test_files/new-file/dummy.ts

@@ -0,0 +1 @@
+export interface Foo {}

src/lib/ng-v5/package.transform.ts

@@ -10,7 +10,8 @@ import {
   startWith,
   debounceTime,
   filter,
-  last
+  takeLast,
+  defaultIfEmpty
 } from 'rxjs/operators';
 import { BuildGraph } from '../brocc/build-graph';
 import { DepthBuilder } from '../brocc/depth';
@@ -224,7 +225,8 @@ const scheduleEntryPoints = (epTransform: Transform): Transform =>
             epTransform
           )
         ),
-        last()
+        takeLast(1), // don't use last as sometimes it this will cause 'no elements in sequence',
+        defaultIfEmpty(graph)
       );
     })
   );