fixed sorting issue

refilc/lib/ui/filter/sort.dart

@@ -1,3 +1,4 @@
+import 'package:flutter/foundation.dart';
 import 'package:refilc/theme/colors/colors.dart';
 import 'package:refilc/ui/date_widget.dart';
 import 'package:refilc/ui/filter/widgets.dart';
@@ -131,6 +132,8 @@ List<Widget> sortDateWidgets(
       elements.insertAll(0, lessonTiles);
 
       final date = (elements + absenceTileWidgets).first.date;
+
+      try {
         items.add(DateWidget(
           date: date,
           widget: Panel(
@@ -144,13 +147,15 @@ List<Widget> sortDateWidgets(
               spawnIsolate: false,
               shrinkWrap: true,
               physics: const NeverScrollableScrollPhysics(),
-            itemBuilder: (context, animation, item, index) => filterItemBuilder(
+              itemBuilder: (context, animation, item, index) =>
+                  filterItemBuilder(
                 context,
                 animation,
                 item.widget,
                 index,
                 len: elements.length,
                 isAfterSeparated: index > 0 &&
+                    index < elements.length &&
                     (elements[index - 1].widget is CertificationCard ||
                         elements[index - 1].widget is NewGradesSurprise),
                 isBeforeSeparated: (index < elements.length - 1) &&
@@ -161,6 +166,11 @@ List<Widget> sortDateWidgets(
             ),
           ),
         ));
+      } catch (e) {
+        if (kDebugMode) {
+          print(e);
+        }
+      }
     }
   }