fix(@schematics/angular): allow insertion when there are no occurrences

Author: hawkgs

packages/schematics/angular/utility/ast-utils.ts

@@ -191,10 +191,7 @@ export function insertAfterLastOccurrence(nodes: ts.Node[],
                                           syntaxKind?: ts.SyntaxKind): Change {
   // sort() has a side effect, so make a copy so that we won't overwrite the parent's object.
   let lastItem = [...nodes].sort(nodesByPosition).pop();
-  if (!lastItem) {
-    throw new Error();
-  }
-  if (syntaxKind) {
+  if (syntaxKind && lastItem) {
     lastItem = findNodes(lastItem, syntaxKind).sort(nodesByPosition).pop();
   }
   if (!lastItem && fallbackPos == undefined) {