diff --git a/README.md b/README.md
index e96e6a2..b3346eb 100644
--- a/README.md
+++ b/README.md
@@ -24,23 +24,22 @@ import 'package:struct_annotation/struct_annotation.dart';
 @Struct()
 class Person {
   final String name;
-  final int age;
 }
 
 void main() {
   // 🪨 Create a const instance with required, name parameters.
-  const jane = Person(name: 'Jane', age: 42);
+  const dash = Person(name: 'Dash');
 
   // 🖨️ Create copies of your object.
-  final john = jane.copyWith(name: 'John');
+  final sparky = dash.copyWith(name: () => 'Sparky');
 
   // ✨ Human-readable string representation.
-  print(jane); // Person(name: Jane, age: 42)
-  print(john); // Person(name: John, age: 42)
+  print(dash); // Person(name: Dash)
+  print(sparky); // Person(name: Sparky)
 
   // ☯️ Value equality comparisons.
-  print(jane == jane.copyWith()); // true
-  print(john == john.copyWith(age: 21)); // false
+  print(dash == dash.copyWith()); // true
+  print(dash == sparky); // false
 }
 ```
 
diff --git a/assets/demo.mp4 b/assets/demo.mp4
deleted file mode 100644
index 34893d2..0000000
Binary files a/assets/demo.mp4 and /dev/null differ
diff --git a/example/main.dart b/example/main.dart
index 7c0d96a..3eb96cd 100644
--- a/example/main.dart
+++ b/example/main.dart
@@ -6,21 +6,20 @@ import 'package:struct_annotation/struct_annotation.dart';
 @Struct()
 class Person {
   final String name;
-  final int age;
 }
 
 void main() {
   // 🪨 Create a const instance with required, name parameters.
-  const jane = Person(name: 'Jane', age: 42);
-  
+  const dash = Person(name: 'Dash');
+
   // 🖨️ Create copies of your object.
-  final john = jane.copyWith(name: 'John');
+  final sparky = dash.copyWith(name: () => 'Sparky');
 
   // ✨ Human-readable string representation.
-  print(jane); // Person(name: Jane, age: 42)
-  print(john); // Person(name: John, age: 42)
+  print(dash); // Person(name: Dash)
+  print(sparky); // Person(name: Sparky)
 
   // ☯️ Value equality comparisons.
-  print(jane == jane.copyWith()); // true
-  print(john == john.copyWith(age: 21)); // false
+  print(dash == dash.copyWith()); // true
+  print(dash == sparky); // false
 }
diff --git a/lib/src/struct_annotation.dart b/lib/src/struct_annotation.dart
index 2eb70ca..7ca465c 100644
--- a/lib/src/struct_annotation.dart
+++ b/lib/src/struct_annotation.dart
@@ -24,7 +24,7 @@ import 'package:macros/macros.dart';
 ///   print(dash); // Person(name: Dash)
 /// 
 ///   // Generated `copyWith`
-///   print(dash.copyWith(name: 'Sparky')); // Person(name: Sparky)
+///   print(dash.copyWith(name: () => 'Sparky')); // Person(name: Sparky)
 /// 
 ///   // Generated `hashCode` and `operator==` for value based equality.
 ///   print(dash == Person(name: 'Dash')); // true
@@ -153,7 +153,7 @@ macro class Struct with _Shared implements ClassDeclarationsMacro, ClassDefiniti
         [
           'external ${clazz.identifier.name} copyWith({',
           for (final field in fields)
-          ...[field.type!.identifier.name, '? ', field.identifier.name, ',']
+          ...[field.type!.identifier.name, if(field.type!.isNullable) '?', ' Function()? ', field.identifier.name, ',']
           ,'});',
         ],
       ),
@@ -330,7 +330,7 @@ macro class Struct with _Shared implements ClassDeclarationsMacro, ClassDefiniti
           clazzName,
           '(',
           for (final field in fields)
-            ...[field.identifier.name,': ', field.identifier.name, ' ?? ', 'this.',field.identifier.name, ','],
+            ...[field.identifier.name, ': ', field.identifier.name, '!= null ? ',field.identifier.name, '.call()', ' : this.',field.identifier.name, ','],
           ');'
         ],
       ),
diff --git a/test/src/struct_annotation_test.dart b/test/src/struct_annotation_test.dart
index da75a0b..e1158c9 100644
--- a/test/src/struct_annotation_test.dart
+++ b/test/src/struct_annotation_test.dart
@@ -25,7 +25,10 @@ void main() {
     });
 
     test('hashCode', () {
-      expect(const EmptyClass().hashCode, equals(const EmptyClass().hashCode));
+      expect(
+        const EmptyClass().hashCode,
+        equals(const EmptyClass().hashCode),
+      );
     });
 
     test('operator==', () {
@@ -53,7 +56,7 @@ void main() {
 
     test('copyWith', () {
       expect(instance.copyWith(), equals(instance));
-      final copy = instance.copyWith(value: 'bye');
+      final copy = instance.copyWith(value: () => 'bye');
       expect(copy, isNot(equals(instance)));
       expect(copy.value, equals('bye'));
     });
@@ -102,7 +105,21 @@ void main() {
     test('copyWith', () {
       expect(nullInstance.copyWith(), equals(nullInstance));
       expect(nonNullInstance.copyWith(), equals(nonNullInstance));
-      final copy = nonNullInstance.copyWith(value: 'bye');
+      expect(nullInstance.copyWith(value: null), equals(nullInstance));
+      expect(nonNullInstance.copyWith(value: null), equals(nonNullInstance));
+      expect(
+        nullInstance.copyWith(value: () => 'hello'),
+        isA<NullableStringFieldClass>().having(
+          (e) => e.value,
+          'value',
+          'hello',
+        ),
+      );
+      expect(
+        nonNullInstance.copyWith(value: () => null),
+        isA<NullableStringFieldClass>().having((e) => e.value, 'value', isNull),
+      );
+      final copy = nonNullInstance.copyWith(value: () => 'bye');
       expect(copy, isNot(equals(nonNullInstance)));
       expect(copy.value, equals('bye'));
     });
@@ -112,8 +129,11 @@ void main() {
         nonNullInstance.hashCode,
         equals(Object.hashAll([nonNullInstance.value])),
       );
-      
-      expect(nullInstance.hashCode, equals(Object.hashAll([nullInstance.value])));
+
+      expect(
+        nullInstance.hashCode,
+        equals(Object.hashAll([nullInstance.value])),
+      );
     });
 
     test('operator==', () {