diff --git a/lib/controllers/providers/api/device_transfer_provider.dart b/lib/controllers/providers/api/device_transfer_provider.dart
index cd38307c..80189f22 100644
--- a/lib/controllers/providers/api/device_transfer_provider.dart
+++ b/lib/controllers/providers/api/device_transfer_provider.dart
@@ -14,7 +14,7 @@ class DeviceTransferProvider extends ChangeNotifier {
 
   //reset provider data
   void reset() {
-    items = null;
+    items.clear();
     nextPage = true;
     stateCode = null;
   }
@@ -28,7 +28,7 @@ class DeviceTransferProvider extends ChangeNotifier {
   bool? nextPage = true;
 
   // list of user requests
-  List<DeviceTransfer>? items;
+  List<DeviceTransfer> items=[];
 
   // when requests in-process _loading = true
   // done _loading = true
@@ -74,11 +74,13 @@ class DeviceTransferProvider extends ChangeNotifier {
         // client's request was successfully received
         List listJson =
             json.decode(utf8.decode(response.bodyBytes).replaceAll("\\", ""));
+        print(listJson);
         List<DeviceTransfer> itemsPage = listJson
             .map((request) => DeviceTransfer.fromJson(request))
             .toList();
-        items ??= [];
-        items?.addAll(itemsPage);
+        print(itemsPage.length);
+        items.clear();
+        items.addAll(itemsPage);
         if (itemsPage.length == pageItemNumber) {
           nextPage = true;
         } else {
diff --git a/lib/models/device/device.dart b/lib/models/device/device.dart
index b5d1f486..e266d366 100644
--- a/lib/models/device/device.dart
+++ b/lib/models/device/device.dart
@@ -30,8 +30,8 @@ class Device {
       id: parsedJson["nid"] ?? parsedJson["id"],
       serialNumber: parsedJson["sn"] ?? parsedJson["value"],
       number: parsedJson["asset_no"],
-      brand: parsedJson["brand"].toString(),
-      model: parsedJson["model"].toString(),
+      brand: parsedJson["brand"] as String?,
+      model: parsedJson["model"] as String?,
       productionDate: getDateFromString(parsedJson["production_date"]),
       supplyDate: getDateFromString(parsedJson["supply_date "]),
       installDate: getDateFromString(parsedJson["install_date "]),
diff --git a/lib/models/lookup.dart b/lib/models/lookup.dart
index 0ddf72f4..805498aa 100644
--- a/lib/models/lookup.dart
+++ b/lib/models/lookup.dart
@@ -31,7 +31,7 @@ class Lookup{
   factory Lookup.fromJson(Map<String,dynamic> parsedJson){
     return Lookup(
       label: parsedJson["value"],
-      id: parsedJson["id"] is int
+      id: parsedJson["id"] is int?
           ? parsedJson["id"]
           : int.tryParse(parsedJson["id"] ?? parsedJson["uid"]),
     );
diff --git a/lib/views/pages/device_transfer/track_device_transfer.dart b/lib/views/pages/device_transfer/track_device_transfer.dart
index 49791085..1daa017d 100644
--- a/lib/views/pages/device_transfer/track_device_transfer.dart
+++ b/lib/views/pages/device_transfer/track_device_transfer.dart
@@ -33,11 +33,12 @@ class _TrackDeviceTransferPageState extends State<TrackDeviceTransferPage>
     _settingProvider = Provider.of<SettingProvider>(context);
     Subtitle? _subtitle = AppLocalization.of(context)?.subtitle;
 
+    //print(_deviceTransferProvider.items.length);
     return Scaffold(
       body: SafeArea(
         child: LoadingManager(
-          isLoading: _deviceTransferProvider.isLoading??false,
-          isFailedLoading: _deviceTransferProvider.items == null,
+          isLoading: _deviceTransferProvider.isLoading,
+          //isFailedLoading: _deviceTransferProvider.items == null,
           stateCode: _deviceTransferProvider.stateCode,
           onRefresh: () async {
             _deviceTransferProvider.reset();
diff --git a/lib/views/pages/user/gas_refill/track_gas_refill.dart b/lib/views/pages/user/gas_refill/track_gas_refill.dart
index 05f92035..16a91f2c 100644
--- a/lib/views/pages/user/gas_refill/track_gas_refill.dart
+++ b/lib/views/pages/user/gas_refill/track_gas_refill.dart
@@ -36,9 +36,9 @@ class _TrackGasRefillPageState extends State<TrackGasRefillPage>
     return Scaffold(
       body: SafeArea(
         child: LoadingManager(
-          isLoading: _gasRefillProvider?.isLoading??false,
+          isLoading: _gasRefillProvider?.isLoading,
           isFailedLoading: _gasRefillProvider?.items == null,
-          stateCode: _gasRefillProvider?.stateCode??0,
+          stateCode: _gasRefillProvider?.stateCode,
           onRefresh: () async {
             _gasRefillProvider?.reset();
             await _gasRefillProvider?.getRequests(
diff --git a/lib/views/widgets/departments/single_department_picker.dart b/lib/views/widgets/departments/single_department_picker.dart
index 6520f5c5..5335fcc9 100644
--- a/lib/views/widgets/departments/single_department_picker.dart
+++ b/lib/views/widgets/departments/single_department_picker.dart
@@ -34,8 +34,8 @@ class _SingleDepartmentPickerState extends State<SingleDepartmentPicker> {
     return Scaffold(
       resizeToAvoidBottomInset: false,
       body: LoadingManager(
-        isLoading: _departmentsProvider?.isLoading??false,
-        stateCode: _departmentsProvider?.stateCode??0,
+        isLoading: _departmentsProvider?.isLoading,
+        stateCode: _departmentsProvider?.stateCode,
         isFailedLoading: _departmentsProvider?.departments == null,
         onRefresh: () async {
           _departmentsProvider?.reset();
diff --git a/lib/views/widgets/hospitals/single_hospital_picker.dart b/lib/views/widgets/hospitals/single_hospital_picker.dart
index 4a99a6a0..f7c2ea34 100644
--- a/lib/views/widgets/hospitals/single_hospital_picker.dart
+++ b/lib/views/widgets/hospitals/single_hospital_picker.dart
@@ -35,8 +35,8 @@ class _SingleHospitalPickerState extends State<SingleHospitalPicker> {
     return Scaffold(
       resizeToAvoidBottomInset: false,
       body: LoadingManager(
-        isLoading: _hospitalsProvider?.isLoading??false,
-        stateCode: _hospitalsProvider?.stateCode??0,
+        isLoading: _hospitalsProvider?.isLoading,
+        stateCode: _hospitalsProvider?.stateCode,
         isFailedLoading: _hospitalsProvider?.hospitals == null,
         onRefresh: () async {
           _hospitalsProvider?.reset();
diff --git a/lib/views/widgets/loaders/loading_manager.dart b/lib/views/widgets/loaders/loading_manager.dart
index 83ce2833..567304e7 100644
--- a/lib/views/widgets/loaders/loading_manager.dart
+++ b/lib/views/widgets/loaders/loading_manager.dart
@@ -9,9 +9,9 @@ import 'failed_loading.dart';
 class LoadingManager extends StatefulWidget {
   final bool? isLoading;
   final bool? isFailedLoading;
-  final bool? isNotPage;
+  final bool isNotPage;
   final int? progress;
-  final bool? askOnBack;
+  final bool askOnBack;
   final int? stateCode;
   final Future<void> Function()? onRefresh;
   final Widget? child;