feature: initial proposal of 'is not null'

lib/src/lucid_validation_builder.dart

@@ -56,13 +56,14 @@ abstract class LucidValidationBuilder<TProp, Entity> {
   final List<RuleFunc<Entity>> _rules = [];
   var _mode = CascadeMode.continueExecution;
   LucidValidator<TProp>? _nestedValidator;
+  LucidValidator _lucid;
 
   bool Function(Entity entity)? _condition;
 
   /// Creates a [LucidValidationBuilder] instance with an optional [key].
   ///
   /// The [key] can be used to identify this specific validation in a larger validation context.
-  LucidValidationBuilder(this.key, this.label, this._selector);
+  LucidValidationBuilder(this.key, this.label, this._selector, this._lucid);
 
   String? Function([String?]) nestedByField(Entity entity, String key) {
     if (_nestedValidator == null) {
@@ -154,6 +155,26 @@ abstract class LucidValidationBuilder<TProp, Entity> {
     return this;
   }
 
+  LucidValidationBuilder<T, Entity> useNotNull<T extends Object>(
+      ValidationException? Function(TProp value, Entity entity) rule) {
+    _rules.add((entity) => rule(_selector(entity), entity));
+
+    final builder =
+        _LucidValidationBuilder<T, Entity>(key, label, (Entity entity) {
+      final value = _selector(entity) as T;
+      return value;
+    }, _lucid);
+
+    this._mode = CascadeMode.stopOnFirstFailure;
+
+    _lucid.addBuilder(builder);
+    return builder;
+  }
+
+  CascadeMode getMode() {
+    return this._mode;
+  }
+
   /// Sets the [CascadeMode] for the validation rules associated with this property.
   ///
   /// The [cascade] method allows you to control the behavior of rule execution when a validation failure occurs.
@@ -261,3 +282,8 @@ abstract class LucidValidationBuilder<TProp, Entity> {
     return exceptions;
   }
 }
+
+class _LucidValidationBuilder<TProp, Entity>
+    extends LucidValidationBuilder<TProp, Entity> {
+  _LucidValidationBuilder(super.key, super.label, super.selector, super.lucid);
+}

lib/src/lucid_validator.dart

@@ -6,6 +6,10 @@ import '../lucid_validation.dart';
 abstract class LucidValidator<E> {
   final List<LucidValidationBuilder<dynamic, E>> _builders = [];
 
+  addBuilder(LucidValidationBuilder<dynamic, E> builder) {
+    this._builders.add(builder);
+  }
+
   /// Registers a validation rule for a specific property of the entity.
   ///
   /// [func] is a function that selects the property from the entity [E].
@@ -22,7 +26,7 @@ abstract class LucidValidator<E> {
       TProp Function(E entity) selector,
       {required String key,
       String label = ''}) {
-    final builder = _LucidValidationBuilder<TProp, E>(key, label, selector);
+    final builder = _LucidValidationBuilder<TProp, E>(key, label, selector, this);
     _builders.add(builder);
 
     return builder;
@@ -89,10 +93,14 @@ abstract class LucidValidator<E> {
   /// }
   /// ```
   ValidationResult validate(E entity) {
-    final exceptions =
-        _builders.fold(<ValidationException>[], (previousErrors, builder) {
-      return previousErrors..addAll(builder.executeRules(entity));
-    });
+    final List<ValidationException> exceptions = [];
+
+    for (var builder in _builders) {
+      exceptions.addAll(builder.executeRules(entity));
+      if(builder.getMode() == CascadeMode.stopOnFirstFailure && exceptions.isNotEmpty) {
+        break;
+      }
+    }
 
     return ValidationResult(
       isValid: exceptions.isEmpty,
@@ -103,5 +111,5 @@ abstract class LucidValidator<E> {
 
 class _LucidValidationBuilder<TProp, Entity>
     extends LucidValidationBuilder<TProp, Entity> {
-  _LucidValidationBuilder(super.key, super.label, super.selector);
+  _LucidValidationBuilder(super.key, super.label, super.selector, super.lucid);
 }

lib/src/validations/is_not_null_validation.dart

@@ -22,8 +22,8 @@ extension IsNotNullValidation<T> on SimpleValidationBuilder<T?> {
   /// String format args:
   /// - **{PropertyName}**: The name of the property.
   ///
-  SimpleValidationBuilder<T?> isNotNull({String? message, String? code}) {
-    return use(
+  SimpleValidationBuilder<String> isNotNull({String? message, String? code}) {
+    return useNotNull(
       (value, entity) {
         if (value != null) return null;
 

test/mocks/mocks.dart

@@ -8,7 +8,7 @@ class UserModel {
   String? description;
   int age = 0;
   String phone = '';
-  String cpf = '';
+  String? cpf = '';
 }
 
 class UserValidator extends LucidValidator<UserModel> {
@@ -27,6 +27,7 @@ class UserValidator extends LucidValidator<UserModel> {
         .customValidPhone('Phone invalid format');
 
     ruleFor((user) => user.cpf, key: 'cpf') //
+        .isNotNull()
         .notEmpty()
         .validCPF();
   }

test/src/validations/valid_cpf_validation_test.dart

@@ -9,9 +9,11 @@ void main() {
 
     validator
         .ruleFor((e) => e.cpf, key: 'cpf') //
+        .isNotNull()
+        .notEmpty()
         .validCPF();
 
-    final user = UserModel()..cpf = '1';
+    final user = UserModel()..cpf =  null;
 
     final result = validator.validate(user);
 
@@ -21,6 +23,6 @@ void main() {
 
     final error = result.exceptions.first;
 
-    expect(error.message, "'cpf' is not a valid CPF.");
+    expect(error.message, "'cpf' must not be null.");
   });
 }