Fix PageList null-safe

@@ -80,7 +80,7 @@ class PdfCatalog extends PdfObject {
 
 
     final widgets = <PdfAnnot>[];
     final widgets = <PdfAnnot>[];
     for (var page in pdfDocument.pdfPageList.pages) {
     for (var page in pdfDocument.pdfPageList.pages) {
-      for (var annot in page!.annotations) {
+      for (var annot in page.annotations) {
         if (annot.annot.subtype == '/Widget') {
         if (annot.annot.subtype == '/Widget') {
           widgets.add(annot);
           widgets.add(annot);
         }
         }

@@ -25,7 +25,7 @@ class PdfPageList extends PdfObject {
   PdfPageList(PdfDocument pdfDocument) : super(pdfDocument, type: '/Pages');
   PdfPageList(PdfDocument pdfDocument) : super(pdfDocument, type: '/Pages');
 
 
   /// This holds the pages
   /// This holds the pages
-  final List<PdfPage?> pages = <PdfPage?>[];
+  final pages = <PdfPage>[];
 
 
   @override
   @override
   void prepare() {
   void prepare() {