diff --git a/lib/data/models/schedule_model.dart b/lib/data/models/schedule_model.dart
index 2379cc246..589f67c03 100644
--- a/lib/data/models/schedule_model.dart
+++ b/lib/data/models/schedule_model.dart
@@ -130,7 +130,8 @@ abstract class ScheduleEntity extends Object
     return actions..addAll(super.getActions(userCompany: userCompany));
   }
 
-  int compareTo(ScheduleEntity? schedule, String sortField, bool sortAscending) {
+  int compareTo(
+      ScheduleEntity? schedule, String sortField, bool sortAscending) {
     int response = 0;
     final scheduleA = sortAscending ? this : schedule;
     final scheduleB = sortAscending ? schedule : this;
@@ -174,9 +175,9 @@ abstract class ScheduleEntity extends Object
   }
 
   @override
-  String? get listDisplayName {
+  String get listDisplayName {
     final localization = AppLocalization.of(navigatorKey.currentContext!)!;
-    return localization.lookup(template);
+    return localization.lookup(template) ?? '';
   }
 
   @override
@@ -204,7 +205,7 @@ abstract class ScheduleParameters
       showPaymentsTable:
           action == ScheduleEntity.TEMPLATE_EMAIL_STATEMENT ? true : null,
       onlyClientsWithInvoices:
-        action == ScheduleEntity.TEMPLATE_EMAIL_STATEMENT ? false : null,
+          action == ScheduleEntity.TEMPLATE_EMAIL_STATEMENT ? false : null,
       showCreditsTable:
           action == ScheduleEntity.TEMPLATE_EMAIL_STATEMENT ? true : null,
       status: action == ScheduleEntity.TEMPLATE_EMAIL_STATEMENT
diff --git a/lib/data/models/transaction_model.dart b/lib/data/models/transaction_model.dart
index 6c0538f1b..66c590466 100644
--- a/lib/data/models/transaction_model.dart
+++ b/lib/data/models/transaction_model.dart
@@ -363,11 +363,12 @@ abstract class TransactionEntity extends Object
   }
 
   @override
-  String? get listDisplayName {
+  String get listDisplayName {
     if (description.isNotEmpty) {
       return description.split('\n').first;
     } else {
-      return AppLocalization.of(navigatorKey.currentContext!)!.transaction;
+      return AppLocalization.of(navigatorKey.currentContext!)!.transaction ??
+          '';
     }
   }
 
diff --git a/lib/ui/app/app_bottom_bar.dart b/lib/ui/app/app_bottom_bar.dart
index 7b06e8696..5d02728e1 100644
--- a/lib/ui/app/app_bottom_bar.dart
+++ b/lib/ui/app/app_bottom_bar.dart
@@ -49,7 +49,7 @@ class AppBottomBar extends StatefulWidget {
   final List<String> sortFields;
   final List<EntityStatus> statuses;
   final Function onCheckboxPressed;
-  final Function(String?)? onSelectedSortField;
+  final Function(String)? onSelectedSortField;
   final Function(EntityState, bool?)? onSelectedState;
   final Function(EntityStatus, bool?)? onSelectedStatus;
   final Function(String)? onSelectedCustom1;
@@ -258,7 +258,7 @@ class _AppBottomBarState extends State<AppBottomBar> {
                                 listUIState.sortField == field) {
                               // Is re-selecting
                               widget.onSelectedSortField!(field);
-                            } else {
+                            } else if (value != null) {
                               widget.onSelectedSortField!(value);
                             }
                           },
diff --git a/lib/ui/app/entity_dropdown.dart b/lib/ui/app/entity_dropdown.dart
index fe9f0e2d0..579d48f80 100644
--- a/lib/ui/app/entity_dropdown.dart
+++ b/lib/ui/app/entity_dropdown.dart
@@ -393,7 +393,7 @@ class _EntityDropdownState extends State<EntityDropdown> {
                                           : kDefaultLightSelectedColor)
                                   : Theme.of(context).cardColor,
                               child: EntityAutocompleteListTile(
-                                onTap: (entity) => onSelected(entity),
+                                onTap: (entity) => onSelected(entity!),
                                 entity: options.elementAt(index),
                                 filter: _filter,
                                 overrideSuggestedAmount:
@@ -550,7 +550,7 @@ class _EntityDropdownDialogState extends State<EntityDropdownDialog> {
         itemCount: matches.length,
         itemBuilder: (BuildContext context, int index) {
           final entityId = matches[index];
-          final entity = widget.entityMap![entityId];
+          final entity = widget.entityMap![entityId]!;
           return EntityAutocompleteListTile(
             entity: entity,
             filter: _filter,
@@ -586,12 +586,12 @@ class EntityAutocompleteListTile extends StatelessWidget {
       this.onTap,
       this.subtitle});
 
-  final SelectableEntity? entity;
-  final Function(SelectableEntity? entity)? onTap;
+  final SelectableEntity entity;
+  final Function(SelectableEntity entity)? onTap;
   final String? filter;
   final String? subtitle;
-  final Function(SelectableEntity?)? overrideSuggestedAmount;
-  final Function(SelectableEntity?)? overrideSuggestedLabel;
+  final Function(SelectableEntity)? overrideSuggestedAmount;
+  final Function(SelectableEntity)? overrideSuggestedLabel;
 
   @override
   Widget build(BuildContext context) {
diff --git a/lib/ui/app/forms/client_picker.dart b/lib/ui/app/forms/client_picker.dart
index 2e9566af5..17ddb46ef 100644
--- a/lib/ui/app/forms/client_picker.dart
+++ b/lib/ui/app/forms/client_picker.dart
@@ -29,7 +29,7 @@ class ClientPicker extends StatelessWidget {
 
   final String? clientId;
   final ClientState clientState;
-  final Function(SelectableEntity) onSelected;
+  final Function(SelectableEntity?) onSelected;
   final Function(Completer<SelectableEntity> completer)? onAddPressed;
   final bool? autofocus;
   final List<String> excludeIds;
diff --git a/lib/ui/app/forms/custom_field.dart b/lib/ui/app/forms/custom_field.dart
index a49e5fb8b..4154ec54a 100644
--- a/lib/ui/app/forms/custom_field.dart
+++ b/lib/ui/app/forms/custom_field.dart
@@ -93,10 +93,12 @@ class _CustomFieldState extends State<CustomField> {
       case kFieldTypeSwitch:
         return BoolDropdownButton(
           onChanged: (value) {
-            _controller!.text = value ? kSwitchValueYes : kSwitchValueNo;
+            _controller!.text =
+                value == true ? kSwitchValueYes : kSwitchValueNo;
             Debouncer.complete();
             if (widget.onChanged != null) {
-              widget.onChanged!(value ? kSwitchValueYes : kSwitchValueNo);
+              widget
+                  .onChanged!(value == true ? kSwitchValueYes : kSwitchValueNo);
             }
           },
           value: widget.value == null ? null : widget.value == kSwitchValueYes,
diff --git a/lib/ui/app/forms/date_picker.dart b/lib/ui/app/forms/date_picker.dart
index 692bdffe6..151154c96 100644
--- a/lib/ui/app/forms/date_picker.dart
+++ b/lib/ui/app/forms/date_picker.dart
@@ -117,7 +117,7 @@ class _DatePickerState extends State<DatePicker> {
 
   @override
   Widget build(BuildContext context) {
-    var label = widget.labelText;
+    var label = widget.labelText ?? '';
     if (widget.message != null && (widget.selectedDate ?? '').isEmpty) {
       label += ' • ${widget.message}';
     }
@@ -130,7 +130,7 @@ class _DatePickerState extends State<DatePicker> {
       keyboardType: TextInputType.text,
       decoration: InputDecoration(
         hintText: widget.hint ?? '',
-        labelText: _pendingValue ?? label ?? '',
+        labelText: _pendingValue ?? label,
         suffixIcon:
             widget.allowClearing && (widget.selectedDate ?? '').isNotEmpty
                 ? IconButton(
diff --git a/lib/ui/app/forms/dynamic_selector.dart b/lib/ui/app/forms/dynamic_selector.dart
index d8f65f7f6..9398b96c3 100644
--- a/lib/ui/app/forms/dynamic_selector.dart
+++ b/lib/ui/app/forms/dynamic_selector.dart
@@ -67,7 +67,7 @@ class DynamicSelector extends StatelessWidget {
       return EntityDropdown(
         labelText: labelText ?? localization!.lookup('$entityType'),
         entityType: entityType,
-        onSelected: (entity) => onChanged!(entity?.id),
+        onSelected: (entity) => onChanged!(entity?.id ?? ''),
         onAddPressed: onAddPressed,
         entityId: entityId,
         entityList: entityIds,
diff --git a/lib/ui/app/forms/vendor_picker.dart b/lib/ui/app/forms/vendor_picker.dart
index 2a651ed88..e31d2436c 100644
--- a/lib/ui/app/forms/vendor_picker.dart
+++ b/lib/ui/app/forms/vendor_picker.dart
@@ -28,7 +28,7 @@ class VendorPicker extends StatelessWidget {
 
   final String vendorId;
   final VendorState vendorState;
-  final Function(SelectableEntity) onSelected;
+  final Function(SelectableEntity?) onSelected;
   final Function(Completer<SelectableEntity> completer) onAddPressed;
   final bool? autofocus;
 
diff --git a/lib/ui/app/menu_drawer_vm.dart b/lib/ui/app/menu_drawer_vm.dart
index a8b2a0f70..58f246c7c 100644
--- a/lib/ui/app/menu_drawer_vm.dart
+++ b/lib/ui/app/menu_drawer_vm.dart
@@ -1,4 +1,6 @@
 // Flutter imports:
+import 'dart:async';
+
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
@@ -138,7 +140,7 @@ class MenuDrawerVM {
               final completer = snackBarCompleter<Null>(
                   context, AppLocalization.of(context)!.addedCompany,
                   shouldPop: true)
-                ..future.then((value) {
+                ..future.then<Null>(() {
                   AppBuilder.of(navigatorKey.currentContext!)!.rebuild();
                 } as FutureOr<Null> Function(Null));
 
diff --git a/lib/ui/app/tables/app_paginated_data_table.dart b/lib/ui/app/tables/app_paginated_data_table.dart
index 25325b404..4333f7d36 100644
--- a/lib/ui/app/tables/app_paginated_data_table.dart
+++ b/lib/ui/app/tables/app_paginated_data_table.dart
@@ -141,7 +141,7 @@ class AppPaginatedDataTable extends StatefulWidget {
   /// checkbox in the heading row.
   ///
   /// See [DataTable.onSelectAll].
-  final ValueSetter<bool>? onSelectAll;
+  final ValueSetter<bool?>? onSelectAll;
 
   /// The height of each row (excluding the row that contains column headings).
   ///
diff --git a/lib/ui/app/tables/entity_list.dart b/lib/ui/app/tables/entity_list.dart
index aded81db4..49b19df96 100644
--- a/lib/ui/app/tables/entity_list.dart
+++ b/lib/ui/app/tables/entity_list.dart
@@ -3,6 +3,7 @@ import 'dart:async';
 import 'dart:math';
 
 // Flutter imports:
+import 'package:built_collection/built_collection.dart';
 import 'package:collection/collection.dart' show IterableNullableExtension;
 import 'package:flutter/material.dart' hide DataRow, DataCell, DataColumn;
 
@@ -116,7 +117,8 @@ class _EntityListState extends State<EntityList> {
     final uiState = state.getUIState(widget.entityType)!;
     dataTableSource.editingId = uiState.editingId;
     dataTableSource.entityList = widget.entityList;
-    dataTableSource.entityMap = state.getEntityMap(widget.entityType) as BuiltMap<String?, BaseEntity?>?;
+    dataTableSource.entityMap = state.getEntityMap(widget.entityType)
+        as BuiltMap<String?, BaseEntity?>?;
 
     // ignore: invalid_use_of_visible_for_testing_member, invalid_use_of_protected_member
     dataTableSource.notifyListeners();
@@ -254,8 +256,8 @@ class _EntityListState extends State<EntityList> {
                           min(_firstRowIndex + rowsPerPage, entityList.length);
                       final entities = entityList
                           .sublist(startIndex, endIndex)
-                          .map<BaseEntity?>(
-                              (String? entityId) => entityMap![entityId] as BaseEntity?)
+                          .map<BaseEntity?>((String? entityId) =>
+                              entityMap![entityId] as BaseEntity?)
                           .where((invoice) =>
                               value != listUIState.isSelected(invoice!.id))
                           .toList();
@@ -285,16 +287,18 @@ class _EntityListState extends State<EntityList> {
                       }),
                     ],
                     source: dataTableSource,
-                    sortColumnIndex:
-                        widget.tableColumns!.contains(listUIState.sortField)
-                            ? widget.tableColumns!.indexOf(listUIState.sortField)
-                            : 0,
+                    sortColumnIndex: widget.tableColumns!
+                            .contains(listUIState.sortField)
+                        ? widget.tableColumns!.indexOf(listUIState.sortField)
+                        : 0,
                     sortAscending: listUIState.sortAscending,
                     rowsPerPage: state.prefState.rowsPerPage,
                     onPageChanged: (row) {
-                      _firstRowIndex = row;
-                      store.dispatch(UpdateLastHistory(
-                          (row / state.prefState.rowsPerPage).floor()));
+                      if (row != null) {
+                        _firstRowIndex = row;
+                        store.dispatch(UpdateLastHistory(
+                            (row / state.prefState.rowsPerPage).floor()));
+                      }
                     },
                     initialFirstRowIndex: _firstRowIndex,
                     availableRowsPerPage: [
@@ -358,8 +362,8 @@ class _EntityListState extends State<EntityList> {
                               min(entityList.length, kMaxEntitiesPerBulkAction);
                           final entities = entityList
                               .sublist(0, endIndex)
-                              .map<BaseEntity?>(
-                                  (entityId) => entityMap![entityId] as BaseEntity?)
+                              .map<BaseEntity?>((entityId) =>
+                                  entityMap![entityId] as BaseEntity?)
                               .toList();
                           handleEntitiesActions(
                               entities, EntityAction.toggleMultiselect);
@@ -466,8 +470,9 @@ class _EntityListState extends State<EntityList> {
                             entities: entities,
                             multiselect: true,
                             completer: Completer<Null>()
-                              ..future.then<dynamic>(
-                                  ((_) => widget.onClearMultiselect()) as FutureOr<dynamic> Function(Null)),
+                              ..future.then<Null>((() =>
+                                      widget.onClearMultiselect())
+                                  as FutureOr<Null> Function(Null)),
                           );
                         },
                         onCancelPressed: (_) => widget.onClearMultiselect(),
diff --git a/lib/ui/auth/login_view.dart b/lib/ui/auth/login_view.dart
index c3b5a0a22..445164769 100644
--- a/lib/ui/auth/login_view.dart
+++ b/lib/ui/auth/login_view.dart
@@ -185,11 +185,11 @@ class _LoginState extends State<LoginView> {
 
     final Completer<Null> completer = Completer<Null>();
     completer.future
-        .then((_) {
+        .then<Null>(() {
       setState(() {
         _loginError = '';
       });
-    } as FutureOr<_> Function(Null))
+    } as FutureOr<Null> Function(Null))
         .catchError((Object error) {
       setState(() {
         _buttonController.reset();
diff --git a/lib/ui/auth/login_vm.dart b/lib/ui/auth/login_vm.dart
index 62a0dac90..658799d37 100644
--- a/lib/ui/auth/login_vm.dart
+++ b/lib/ui/auth/login_vm.dart
@@ -115,10 +115,8 @@ class LoginVM {
       onMicrosoftSignUpPressed;
 
   final Function(BuildContext, Completer<Null> completer,
-      {String url,
-      String? secret,
-      String? oneTimePassword}) onAppleLoginPressed;
-  final Function(BuildContext, Completer<Null> completer, String? url)
+      {String url, String secret, String oneTimePassword}) onAppleLoginPressed;
+  final Function(BuildContext, Completer<Null> completer, String url)
       onAppleSignUpPressed;
 
   static LoginVM fromStore(Store<AppState> store) {
@@ -164,9 +162,9 @@ class LoginVM {
       onGoogleLoginPressed: (
         BuildContext context,
         Completer<Null> completer, {
-        required String url,
-        required String secret,
-        required String oneTimePassword,
+        String url = '',
+        String secret = '',
+        String oneTimePassword = '',
       }) async {
         try {
           await GoogleOAuth.signOut();
@@ -286,9 +284,9 @@ class LoginVM {
       onAppleLoginPressed: (
         BuildContext context,
         Completer<Null> completer, {
-        required String url,
-        required String secret,
-        required String oneTimePassword,
+        String url = '',
+        String secret = '',
+        String oneTimePassword = '',
       }) async {
         try {
           final credentials = await SignInWithApple.getAppleIDCredential(
diff --git a/lib/ui/company_gateway/company_gateway_screen.dart b/lib/ui/company_gateway/company_gateway_screen.dart
index b8e85da5a..179623fae 100644
--- a/lib/ui/company_gateway/company_gateway_screen.dart
+++ b/lib/ui/company_gateway/company_gateway_screen.dart
@@ -72,8 +72,9 @@ class CompanyGatewayScreen extends StatelessWidget {
                       entities: companyGateways,
                       multiselect: true,
                       completer: Completer<Null>()
-                        ..future.then<dynamic>(((_) =>
-                            store.dispatch(ClearCompanyGatewayMultiselect())) as FutureOr<dynamic> Function(Null)),
+                        ..future.then<Null>((() => store
+                                .dispatch(ClearCompanyGatewayMultiselect()))
+                            as FutureOr<Null> Function(Null)),
                     );
                   },
             onCancelPressed: (context) =>
diff --git a/lib/ui/invoice/edit/invoice_edit_details_vm.dart b/lib/ui/invoice/edit/invoice_edit_details_vm.dart
index 5d50ba50e..f98352190 100644
--- a/lib/ui/invoice/edit/invoice_edit_details_vm.dart
+++ b/lib/ui/invoice/edit/invoice_edit_details_vm.dart
@@ -68,7 +68,7 @@ class EntityEditDetailsVM {
   final Function(InvoiceEntity)? onChanged;
   final Function(BuildContext context, InvoiceEntity, ClientEntity?)?
       onClientChanged;
-  final Function(BuildContext context, InvoiceEntity, VendorEntity)?
+  final Function(BuildContext context, InvoiceEntity, VendorEntity?)?
       onVendorChanged;
   final BuiltMap<String?, ClientEntity?>? clientMap;
   final BuiltList<String>? clientList;
diff --git a/lib/ui/invoice/edit/invoice_edit_items_vm.dart b/lib/ui/invoice/edit/invoice_edit_items_vm.dart
index 8f7fb5011..994f913c6 100644
--- a/lib/ui/invoice/edit/invoice_edit_items_vm.dart
+++ b/lib/ui/invoice/edit/invoice_edit_items_vm.dart
@@ -67,7 +67,7 @@ class EntityEditItemsVM {
   final int? invoiceItemIndex;
   final Function? addLineItem;
   final Function? deleteLineItem;
-  final Function(int?)? onRemoveInvoiceItemPressed;
+  final Function(int)? onRemoveInvoiceItemPressed;
   final Function? clearSelectedInvoiceItem;
   final Function(InvoiceItemEntity, int?)? onChangedInvoiceItem;
   final Function(int, int)? onMovedInvoiceItem;
diff --git a/lib/ui/settings/localization_vm.dart b/lib/ui/settings/localization_vm.dart
index 5fdca2a92..4dc35ac91 100644
--- a/lib/ui/settings/localization_vm.dart
+++ b/lib/ui/settings/localization_vm.dart
@@ -75,14 +75,14 @@ class LocalizationSettingsVM {
                 final appBuilder = AppBuilder.of(context);
                 final completer = snackBarCompleter<Null>(
                     context, AppLocalization.of(context)!.savedSettings)
-                  ..future.then<dynamic>((value) {
+                  ..future.then<Null>(() {
                     appBuilder!.rebuild();
                     store.dispatch(RefreshData(
                         includeStatic: true,
                         completer: Completer<dynamic>()
                           ..future
                               .then((dynamic value) => appBuilder.rebuild())));
-                  } as FutureOr<dynamic> Function(Null));
+                  } as FutureOr<Null> Function(Null));
                 store.dispatch(SaveCompanyRequest(
                     completer: completer, company: settingsUIState.company));
                 break;
diff --git a/lib/ui/task_status/task_status_screen.dart b/lib/ui/task_status/task_status_screen.dart
index 205a333c5..463a05981 100644
--- a/lib/ui/task_status/task_status_screen.dart
+++ b/lib/ui/task_status/task_status_screen.dart
@@ -78,8 +78,9 @@ class TaskStatusScreen extends StatelessWidget {
                 entities: taskStatusIds,
                 multiselect: true,
                 completer: Completer<Null>()
-                  ..future.then<dynamic>(
-                      ((_) => store.dispatch(ClearTaskStatusMultiselect())) as FutureOr<dynamic> Function(Null)),
+                  ..future.then<Null>((() =>
+                          store.dispatch(ClearTaskStatusMultiselect()))
+                      as FutureOr<Null> Function(Null)),
               );
             },
             label: localization!.actions,