fix: handle nullable duration for breaks and correctly update breaks

packages/flutter_availability/lib/src/ui/view_models/break_view_model.dart

@@ -33,6 +33,14 @@ class BreakViewModel {
   /// [endTime]
   final Duration? duration;
 
+  /// Get the duration in minutes
+  /// If the duration is null, return the difference between the start and end
+  /// time in minutes
+  int get durationInMinutes =>
+      duration?.inMinutes ??
+      ((endTime!.hour * 60 + endTime!.minute) -
+          (startTime!.hour * 60 + startTime!.minute));
+
   /// Returns true if the break is valid
   /// The start is before the end and the duration is equal or lower than the
   /// difference between the start and end

packages/flutter_availability/lib/src/ui/widgets/pause_selection.dart

@@ -56,8 +56,9 @@ class PauseSelection extends StatelessWidget {
     Future<void> onEditBreak(BreakViewModel availabilityBreak) async {
       var updatedBreak = await openBreakDialog(availabilityBreak);
       if (updatedBreak == null) return;
-
+      // remove the old break and add the updated one
       var updatedBreaks = [...breaks, updatedBreak];
+      updatedBreaks.remove(availabilityBreak);
       onBreaksChanged(updatedBreaks);
     }
 
@@ -145,6 +146,8 @@ class BreakDisplay extends StatelessWidget {
       breakModel.endTime!,
     );
 
+    var breakDuration = breakModel.durationInMinutes;
+
     return InkWell(
       onTap: onClick,
       child: Container(
@@ -157,7 +160,7 @@ class BreakDisplay extends StatelessWidget {
         child: Row(
           children: [
             Text(
-              "${breakModel.duration!.inMinutes} "
+              "$breakDuration "
               "${translations.timeMinutes}  |  "
               "$starTime - "
               "$endTime",
@@ -267,9 +270,10 @@ class _AvailabilityBreakSelectionDialogState
         ? () {
             if (_breakViewModel.isValid) {
               Navigator.of(context).pop(_breakViewModel);
+            } else {
+              debugPrint("Break is not valid");
+              // TODO(freek): show error message
             }
-            debugPrint("Break is not valid");
-            // TODO(freek): show error message
           }
         : null;