Move down to only 1 abstract data type with a nully Frequency. Should aid in making the Expense page usable for all 3 data type.

lib/models/asset.dart

@@ -1,6 +1,7 @@
-import '/models/tracked_type.dart';
+// Local
+import '/models/tracked_item.dart';
 
-class Asset extends TrackedType {
+class Asset extends TrackedItem {
   static String amountText = "Amount";
 
   Asset({

lib/models/database_backup.dart

@@ -29,7 +29,7 @@ class DatabaseBackup {
             'id': e.id,
             'name': e.name,
             'cost': e.amount,
-            'frequency': e.frequency.title,
+            'frequency': e.frequency!.title,
             'description': e.description,
           },
       ],
@@ -39,7 +39,7 @@ class DatabaseBackup {
             'id': i.id,
             'name': i.name,
             'revenue': i.amount,
-            'frequency': i.frequency.title,
+            'frequency': i.frequency!.title,
             'description': i.description,
           },
       ],

lib/models/expense.dart

@@ -1,8 +1,8 @@
 // Local
-import '/models/tracked_type_recurring.dart';
+import '/models/tracked_item.dart';
 import '/models/frequency.dart';
 
-class Expense extends RecurringTrackedType {
+class Expense extends TrackedItem {
   static String amountText = "Cost";
 
   Expense({
@@ -29,7 +29,7 @@ class Expense extends RecurringTrackedType {
       'id': id,
       'name': name,
       'cost': amount,
-      'frequency': frequency.title,
+      'frequency': frequency!.title,
       'description': description,
     };
   }

lib/models/income.dart

@@ -1,8 +1,8 @@
 // Local
-import '/models/tracked_type_recurring.dart';
+import '/models/tracked_item.dart';
 import '/models/frequency.dart';
 
-class Income extends RecurringTrackedType {
+class Income extends TrackedItem {
   static String amountText = "Revenue";
 
   Income({
@@ -29,7 +29,7 @@ class Income extends RecurringTrackedType {
       'id': id,
       'name': name,
       'revenue': amount,
-      'frequency': frequency.title,
+      'frequency': frequency!.title,
       'description': description,
     };
   }

lib/models/tracked_item.dart

@@ -0,0 +1,49 @@
+// Local
+import '/models/frequency.dart';
+
+abstract class TrackedItem {
+  int? id;
+  String name;
+  double amount;
+  Frequency? frequency;
+  String description;
+
+  TrackedItem({
+    this.id,
+    required this.name,
+    required this.amount,
+    this.frequency,
+    required this.description,
+  });
+
+  static String amountText = "Amount";
+  String getAmountText() => amountText;
+
+  @override
+  String toString() {
+    return toMap().toString();
+  }
+
+  double calcComparableAmountYearly() {
+    return frequency == null ? 0 : amount * frequency!.timesPerYear;
+  }
+
+  double calcComparableAmountDaily() {
+    return frequency == null ? 0 : amount / frequency!.numDays;
+  }
+
+  Map<String, dynamic> toMap() {
+    return frequency == null ? {
+      'id': id,
+      'name': name,
+      'amount': amount,
+      'description': description,
+    } : {
+      'id': id,
+      'name': name,
+      'amount': amount,
+      'frequency': frequency!.title,
+      'description': description,
+    };
+  }
+}

lib/models/tracked_type.dart

@@ -1,30 +0,0 @@
-abstract class TrackedType {
-  int? id;
-  String name;
-  double amount;
-  String description;
-
-  TrackedType({
-    this.id,
-    required this.name,
-    required this.amount,
-    required this.description,
-  });
-
-  static String amountText = "Amount";
-  String getAmountText() => amountText;
-
-  @override
-  String toString() {
-    return toMap().toString();
-  }
-
-  Map<String, dynamic> toMap() {
-    return {
-      'id': id,
-      'name': name,
-      'amount': amount,
-      'description': description,
-    };
-  }
-}

lib/models/tracked_type_recurring.dart

@@ -1,34 +0,0 @@
-// Local
-import '/models/tracked_type.dart';
-import '/models/frequency.dart';
-
-abstract class RecurringTrackedType extends TrackedType {
-  Frequency frequency;
-
-  RecurringTrackedType({
-    super.id,
-    required super.name,
-    required super.amount,
-    required this.frequency,
-    required super.description,
-  });
-
-  double calcComparableAmountYearly() {
-    return amount * frequency.timesPerYear;
-  }
-
-  double calcComparableAmountDaily() {
-    return amount / frequency.numDays;
-  }
-
-  @override
-  Map<String, dynamic> toMap() {
-    return {
-      'id': id,
-      'name': name,
-      'amount': amount,
-      'frequency': frequency.title,
-      'description': description,
-    };
-  }
-}