update pubspec

lib/pagination/paginator_listview.dart

@@ -10,19 +10,17 @@ typedef OnScroll = void Function(bool down);
 class PaginatorListView<T> extends StatelessWidget {
   final PaginatorListener<T> paginatorListener;
   final RowBuilder rowBuilder;
-  final OnScroll onScroll;
+  final OnScroll? onScroll;
   final ScrollController _scrollController;
   final Color color;
 
   PaginatorListView(
-      {Key key,
-      this.paginatorListener,
-      this.rowBuilder,
+      {Key? key,
+      required this.paginatorListener,
+      required this.rowBuilder,
       this.onScroll,
       this.color = Colors.blueAccent})
       : _scrollController = ScrollController(),
-        assert(paginatorListener != null),
-        assert(rowBuilder != null),
         super(key: key) {
     _scrollController.addListener(() async {
       if (_scrollController.position.pixels ==
@@ -32,7 +30,7 @@ class PaginatorListView<T> extends StatelessWidget {
       if (onScroll != null) {
         var down = _scrollController.position.userScrollDirection ==
             ScrollDirection.forward;
-        onScroll(down);
+        onScroll!(down);
       }
     });
   }