Make transformed schema callbacks non-nullable

example/lib/schema_types_transforms.dart

@@ -16,7 +16,7 @@ class TagList {
 final baseColorSchema = Ack.string();
 
 @AckType()
-final colorSchema = Ack.string().transform<Color>((value) => Color(value!));
+final colorSchema = Ack.string().transform<Color>((value) => Color(value));
 
 @AckType()
 final profileSchema = Ack.object({
@@ -25,14 +25,14 @@ final profileSchema = Ack.object({
   'lastLogin': Ack.datetime(),
   'timeout': Ack.duration(),
   'links': Ack.list(Ack.uri()),
-  'favoriteColor': Ack.string().transform<Color>((value) => Color(value!)),
-  'slug': Ack.string().transform<String>((value) => value! + '#'),
+  'favoriteColor': Ack.string().transform<Color>((value) => Color(value)),
+  'slug': Ack.string().transform<String>((value) => value + '#'),
   'accent': colorSchema,
   'colors': Ack.list(colorSchema),
   'customColors': Ack.list(
-    baseColorSchema.transform<Color>((value) => Color(value!)),
+    baseColorSchema.transform<Color>((value) => Color(value)),
   ),
   'tagList': Ack.list(
     Ack.string(),
-  ).transform<TagList>((value) => TagList(value!)),
+  ).transform<TagList>((value) => TagList(value)),
 });

llms.txt

@@ -270,20 +270,27 @@ final signupSchema = Ack.object({
 
 ### Transformations
 
-Transform converts validated data to a different type. The transformer receives a **nullable** value (`T?`) because the underlying schema might be nullable:
+Transform converts validated data to a different type. The transformer
+receives a **non-null** value (`T`) after validation. If a nullable schema
+accepts `null`, that `null` passes through without invoking the transformer:
 
 ```dart
-// Transform string to DateTime (value is non-null after validation, so use !)
+// Transform string to DateTime
 final dateSchema = Ack.string()
   .minLength(10)
-  .transform<DateTime>((value) => DateTime.parse(value!));
+  .transform<DateTime>((value) => DateTime.parse(value));
+
+// Nullable inputs bypass the transformer and stay null
+final optionalDateSchema = Ack.string()
+  .nullable()
+  .transform<DateTime>((value) => DateTime.parse(value));
 
 // Add computed fields to objects
 final userWithAge = Ack.object({
   'name': Ack.string(),
   'birthYear': Ack.integer(),
 }).transform<Map<String, Object?>>((data) {
-  final birthYear = data!['birthYear'] as int;
+  final birthYear = data['birthYear'] as int;
   return {...data, 'age': DateTime.now().year - birthYear};
 });
 ```

packages/ack/lib/src/ack.dart

@@ -79,7 +79,7 @@ final class Ack {
   static TransformedSchema<String, DateTime> date() {
     return string()
         .date() // Validates ISO 8601 date format (YYYY-MM-DD) first
-        .transform<DateTime>((s) => DateTime.parse(s!));
+        .transform<DateTime>((s) => DateTime.parse(s));
   }
 
   /// Creates a datetime schema that parses ISO 8601 datetime strings into DateTime objects.
@@ -98,7 +98,7 @@ final class Ack {
   static TransformedSchema<String, DateTime> datetime() {
     return string()
         .datetime() // Validates ISO 8601 datetime format with timezone first
-        .transform<DateTime>((s) => DateTime.parse(s!));
+        .transform<DateTime>((s) => DateTime.parse(s));
   }
 
   /// Creates a schema that parses URI strings into [Uri] objects.
@@ -115,7 +115,7 @@ final class Ack {
   static TransformedSchema<String, Uri> uri() {
     return string()
         .uri() // Validates URI format first
-        .transform<Uri>((s) => Uri.parse(s!));
+        .transform<Uri>((s) => Uri.parse(s));
   }
 
   /// Creates a schema that parses millisecond integers into [Duration] objects.
@@ -131,6 +131,6 @@ final class Ack {
   /// final timeout = Ack.duration().min(Duration(minutes: 1)).max(Duration(minutes: 2));
   /// ```
   static TransformedSchema<int, Duration> duration() {
-    return integer().transform<Duration>((ms) => Duration(milliseconds: ms!));
+    return integer().transform<Duration>((ms) => Duration(milliseconds: ms));
   }
 }

packages/ack/lib/src/schemas/discriminated_object_schema.dart

@@ -26,11 +26,11 @@ Object? _serializeJsonSchemaDefaultOrNull(Object? defaultValue) {
 ///     'cat': Ack.object({
 ///       'type': Ack.literal('cat'),
 ///       'name': Ack.string(),
-///     }).transform<Animal>((map) => Cat(map!['name'] as String)),
+///     }).transform<Animal>((map) => Cat(map['name'] as String)),
 ///     'dog': Ack.object({
 ///       'type': Ack.literal('dog'),
 ///       'name': Ack.string(),
-///     }).transform<Animal>((map) => Dog(map!['name'] as String)),
+///     }).transform<Animal>((map) => Dog(map['name'] as String)),
 ///   },
 /// );
 /// ```

packages/ack/lib/src/schemas/extensions/ack_schema_extensions.dart

@@ -60,11 +60,15 @@ extension AckSchemaExtensions<T extends Object> on AckSchema<T> {
 
   /// Transforms the validated value using the provided transformer function.
   ///
-  /// The transformer receives `T?` because the base schema may be nullable or
-  /// optional, meaning `null` is a valid validated value.
-  /// This is useful for converting data types or applying business logic transformations.
+  /// The [transformer] always receives a non-null `T` value. Even when this
+  /// schema is nullable, the transformer is only called for non-null values; if
+  /// the input is `null`, it passes through as `null` without invoking the
+  /// transformer.
+  ///
+  /// This is useful for converting data types or applying business logic
+  /// transformations without defensively handling `null` inside the callback.
   TransformedSchema<T, R> transform<R extends Object>(
-    R Function(T? value) transformer,
+    R Function(T value) transformer,
   ) {
     return TransformedSchema(
       this,

packages/ack/lib/src/schemas/extensions/string_schema_extensions.dart

@@ -142,18 +142,18 @@ extension StringSchemaExtensions on StringSchema {
   /// Trims leading and trailing whitespace from the string before validation.
   /// Returns a transformed schema that applies String.trim() to the input.
   TransformedSchema<String, String> trim() {
-    return transform((s) => s?.trim() ?? '');
+    return transform((s) => s.trim());
   }
 
   /// Converts the string to lowercase after validation.
   /// Returns a transformed schema that applies String.toLowerCase() to the input.
   TransformedSchema<String, String> toLowerCase() {
-    return transform((s) => s?.toLowerCase() ?? '');
+    return transform((s) => s.toLowerCase());
   }
 
   /// Converts the string to uppercase after validation.
   /// Returns a transformed schema that applies String.toUpperCase() to the input.
   TransformedSchema<String, String> toUpperCase() {
-    return transform((s) => s?.toUpperCase() ?? '');
+    return transform((s) => s.toUpperCase());
   }
 }

packages/ack/lib/src/schemas/transformed_schema.dart

@@ -9,7 +9,7 @@ part of 'schema.dart';
 /// // Parse ISO date strings into DateTime objects
 /// final dateSchema = Ack.string()
 ///   .datetime()
-///   .transform<DateTime>((s) => DateTime.parse(s!));
+///   .transform<DateTime>((s) => DateTime.parse(s));
 /// ```
 ///
 /// ## Default Values
@@ -21,7 +21,7 @@ part of 'schema.dart';
 /// ```dart
 /// // This works - primitive defaults are safely cloned
 /// final schema = Ack.string()
-///     .transform((v) => v ?? 'fallback')
+///     .transform((v) => v)
 ///     .copyWith(defaultValue: 'hello');
 ///
 /// // Limitation: List<String> defaults may not be cloned (mutation risk)
@@ -35,7 +35,7 @@ part of 'schema.dart';
 class TransformedSchema<InputType extends Object, OutputType extends Object>
     extends AckSchema<OutputType> {
   final AckSchema<InputType> schema;
-  final OutputType Function(InputType?) transformer;
+  final OutputType Function(InputType) transformer;
 
   TransformedSchema(
     this.schema,
@@ -75,6 +75,19 @@ class TransformedSchema<InputType extends Object, OutputType extends Object>
     }
 
     final validatedValue = originalResult.getOrNull();
+
+    // Null passes through without hitting the transformer when this schema
+    // itself is nullable. Outer nullability still applies even if the wrapped
+    // schema can accept null. Constraints and refinements on the transformed
+    // schema are typed OutputType (extends Object) and cannot accept null,
+    // so they must be skipped here.
+    if (validatedValue == null) {
+      if (!isNullable) {
+        return failNonNullable(context);
+      }
+      return SchemaResult.ok(null);
+    }
+
     try {
       final transformedValue = transformer(validatedValue);
 

packages/ack/test/converters/ack_to_json_schema_model_test.dart

@@ -87,10 +87,10 @@ void main() {
         schemas: {
           'cat': Ack.object({
             'name': Ack.string(),
-          }).transform<String>((map) => map!['name'] as String),
+          }).transform<String>((map) => map['name'] as String),
           'dog': Ack.object({
             'name': Ack.string(),
-          }).transform<String>((map) => map!['name'] as String),
+          }).transform<String>((map) => map['name'] as String),
         },
       );
 
@@ -115,7 +115,7 @@ void main() {
           discriminatorKey: 'type',
           schemas: {
             'cat': Ack.object({'name': Ack.string()})
-                .transform<String>((map) => map!['name'] as String)
+                .transform<String>((map) => map['name'] as String)
                 .copyWith(description: 'cat branch'),
           },
         );

packages/ack/test/documentation/advanced_features_test.dart

@@ -102,7 +102,7 @@ void main() {
         final dateSchema = Ack.string()
             .matches(r'^\d{4}-\d{2}-\d{2}$')
             .transform<DateTime>((dateStr) {
-              return DateTime.parse(dateStr!);
+              return DateTime.parse(dateStr);
             });
 
         final result = dateSchema.safeParse('2024-01-15');
@@ -119,7 +119,7 @@ void main() {
             .matches(r'^[\d\s\-\(\)\+]+$')
             .transform((phone) {
               // Remove all non-digit characters except +
-              return phone!.replaceAll(RegExp(r'[^\d\+]'), '');
+              return phone.replaceAll(RegExp(r'[^\d\+]'), '');
             });
 
         final result = phoneSchema.safeParse('+1 (555) 123-4567');

packages/ack/test/documentation/core_concepts_schemas_examples_test.dart

@@ -401,7 +401,7 @@ void main() {
 
       test('transform examples adjust output data', () {
         final upperSchema = Ack.string().transform(
-          (s) => s?.toUpperCase() ?? '',
+          (s) => s.toUpperCase(),
         );
         expect(upperSchema.safeParse('hello').getOrThrow(), equals('HELLO'));
 
@@ -410,7 +410,7 @@ void main() {
               'name': Ack.string(),
               'birthYear': Ack.integer(),
             }).transform((data) {
-              final birthYear = data!['birthYear'] as int;
+              final birthYear = data['birthYear'] as int;
               final age = DateTime.now().year - birthYear;
               return {...data, 'age': age};
             });
@@ -425,7 +425,7 @@ void main() {
 
         final dateSchema = Ack.string()
             .matches(r'^\d{4}-\d{2}-\d{2}$')
-            .transform<DateTime>((s) => DateTime.parse(s!));
+            .transform<DateTime>((s) => DateTime.parse(s));
         final parsedDate =
             dateSchema.safeParse('2024-01-01').getOrThrow() as DateTime;
         expect(parsedDate.year, equals(2024));

packages/ack/test/documentation/overview_doc_examples_test.dart

@@ -180,7 +180,7 @@ void main() {
             'name': Ack.string(),
             'birthYear': Ack.integer(),
           }).transform((data) {
-            final birthYear = data!['birthYear'] as int;
+            final birthYear = data['birthYear'] as int;
             final age = DateTime.now().year - birthYear;
             return {...data, 'age': age};
           });

packages/ack/test/documentation/social_media_demos_test.dart

@@ -10,7 +10,7 @@ void main() {
               'name': Ack.string(),
               'birthYear': Ack.integer().min(1900).max(2024),
             }).transform((data) {
-              final age = DateTime.now().year - (data!['birthYear'] as int);
+              final age = DateTime.now().year - (data['birthYear'] as int);
               return {...data, 'age': age};
             });
 
@@ -29,7 +29,7 @@ void main() {
               'name': Ack.string(),
               'birthYear': Ack.integer().min(1900).max(2024),
             }).transform((data) {
-              final age = DateTime.now().year - (data!['birthYear'] as int);
+              final age = DateTime.now().year - (data['birthYear'] as int);
               return {...data, 'age': age};
             });
 

packages/ack/test/integration/complex_schema_test.dart

@@ -20,7 +20,7 @@ void main() {
             'quantity': Ack.integer().positive(),
           }).transform<Map<String, Object?>>((product) {
             return {
-              ...product!,
+              ...product,
               'total':
                   (product['price'] as double) * (product['quantity'] as int),
             };
@@ -66,7 +66,7 @@ void main() {
               }, message: 'Order total must be positive')
               .transform<Map<String, Object?>>((order) {
                 // Calculate order summary
-                final items = order!['items'] as List;
+                final items = order['items'] as List;
                 final subtotal = items.fold<double>(
                   0,
                   (sum, item) => sum + (item as Map)['total'],
@@ -141,7 +141,7 @@ void main() {
               .partial() // Make all fields optional
               .transform<Map<String, Object?>>((obj) {
                 // Handle missing data gracefully
-                final data = obj!['data'] as Map<String, Object?>?;
+                final data = obj['data'] as Map<String, Object?>?;
                 return {
                   'hasData': data != null,
                   'value': data?['value'] ?? 'default',
@@ -182,7 +182,7 @@ void main() {
                 'profile': Ack.object({'age': Ack.integer().min(18)}),
               }),
             },
-          ).transform<Map<String, Object?>>((data) => data!).refine((data) {
+          ).transform<Map<String, Object?>>((data) => data).refine((data) {
             final profile = data['profile'] as Map;
             return (profile['age'] as int) < 100;
           }, message: 'Age too high');