diff --git a/lib/src/localization/language.dart b/lib/src/localization/language.dart
index 18b6cbc..edc6b7b 100644
--- a/lib/src/localization/language.dart
+++ b/lib/src/localization/language.dart
@@ -35,8 +35,8 @@ abstract class Language {
     code.equalTo: "'{PropertyName}' must be equal to '{ComparisonValue}'.",
     code.greaterThan: "'{PropertyName}' must be greater than '{ComparisonValue}'.",
     code.isEmpty: "'{PropertyName}' must be empty.",
-    code.isNotNull: "'{PropertyName}' must not be empty.",
-    code.isNull: "'{PropertyName}' must be empty.",
+    code.isNotNull: "'{PropertyName}' must not be null.",
+    code.isNull: "'{PropertyName}' must be null.",
     code.lessThan: "'{PropertyName}' must be less than '{ComparisonValue}'.",
     code.matchesPattern: "'{PropertyName}' is not in the correct format.",
     code.max: "'{PropertyName}' must be less than or equal to {MaxValue}. You entered {PropertyValue}.",
diff --git a/lib/src/validations/is_null_validation.dart b/lib/src/validations/is_null_validation.dart
index c519509..33f9732 100644
--- a/lib/src/validations/is_null_validation.dart
+++ b/lib/src/validations/is_null_validation.dart
@@ -18,11 +18,25 @@ extension IsNullValidation<T> on SimpleValidationBuilder<T?> {
   /// ruleFor((user) => user.name, key: 'name') // optional field
   ///   .isNull();
   /// ```
-  SimpleValidationBuilder<T?> isNull({String message = 'Must be null', String code = 'must_be_null'}) {
-    return must(
-      (value) => value == null,
-      message,
-      code,
+  /// String format args:
+  /// - **{PropertyName}**: The name of the property.
+  ///
+  SimpleValidationBuilder<T?> isNull({String? message, String? code}) {
+    return use(
+      (value, entity) {
+        if (value == null) return null;
+
+        final currentCode = code ?? Language.code.isNull;
+        final currentMessage = LucidValidation.global.languageManager.translate(
+          currentCode,
+          parameters: {
+            'PropertyName': key,
+          },
+          defaultMessage: message,
+        );
+
+        return ValidationError(message: currentMessage, code: currentCode);
+      },
     );
   }
 }
diff --git a/test/mocks/mocks.dart b/test/mocks/mocks.dart
index 00ad340..44d6fc6 100644
--- a/test/mocks/mocks.dart
+++ b/test/mocks/mocks.dart
@@ -5,6 +5,7 @@ class UserModel {
   String email = '';
   String password = '';
   String confirmPassword = '';
+  String? description;
   int age = 0;
   String phone = '';
 }
diff --git a/test/src/validations/is_not_null_validation_test.dart b/test/src/validations/is_not_null_validation_test.dart
new file mode 100644
index 0000000..a876ba5
--- /dev/null
+++ b/test/src/validations/is_not_null_validation_test.dart
@@ -0,0 +1,25 @@
+import 'package:lucid_validation/lucid_validation.dart';
+import 'package:test/test.dart';
+
+import '../../mocks/mocks.dart';
+
+void main() {
+  test('is not null validation ...', () {
+    final validator = TestLucidValidator<UserModel>();
+    validator
+        .ruleFor((e) => e.description, key: 'description') //
+        .isNotNull();
+
+    final user = UserModel();
+
+    final result = validator.validate(user);
+
+    expect(result.isValid, false);
+
+    expect(result.errors.length, 1);
+
+    final error = result.errors.first;
+
+    expect(error.message, r"'description' must not be null.");
+  });
+}
diff --git a/test/src/validations/is_null_validation_test.dart b/test/src/validations/is_null_validation_test.dart
new file mode 100644
index 0000000..09d81de
--- /dev/null
+++ b/test/src/validations/is_null_validation_test.dart
@@ -0,0 +1,26 @@
+import 'package:lucid_validation/lucid_validation.dart';
+import 'package:test/test.dart';
+
+import '../../mocks/mocks.dart';
+
+void main() {
+  test('is null validation ...', () {
+    final validator = TestLucidValidator<UserModel>();
+
+    validator
+        .ruleFor((e) => e.description, key: 'description') //
+        .isNull();
+
+    final user = UserModel()..description = 'description';
+
+    final result = validator.validate(user);
+
+    expect(result.isValid, false);
+
+    expect(result.errors.length, 1);
+
+    final error = result.errors.first;
+
+    expect(error.message, r"'description' must be null.");
+  });
+}