Nullable

Nullable validator are used to represent a value that may or may not be present.

How it works

The nullable validator is a wrapper around another type. It allows the value to be null in addition to the normal values of the wrapped type.

import 'package:acanthis/acanthis.dart';

void main() {
  final schema = string().nullable();

  final result = schema.tryParse(null);

  if (result.success) {
	print('The schema is valid!');
  } else {
	print('The schema is invalid!');
  }
}

In this example, the schema is a nullable string. The tryParse method is called with null as the argument. Since the schema is nullable, the result is successful.

TIP

The AcanthisParseResult object, that is returned by the parse and tryParse method is described here.

Default value

You can also specify a default value for the nullable type.

import 'package:acanthis/acanthis.dart';

void main() {
  final schema = string().nullable(defaultValue: 'default');

  final result = schema.tryParse(null);

  if (result.success) {
	print('The schema is valid!');
  } else {
	print('The schema is invalid!');
  }
  assert(result.value == 'default');
}

And for Maps or Lists?

The nullable type can be used with maps and lists as well.

nullable_map.dart

import 'package:acanthis/acanthis.dart';

void main() {
  final schema = object({
	'name': string().min(3),
	'age': number().positive(),
  }).nullable();

  final result = schema.tryParse(null);

  if (result.success) {
	print('The schema is valid!');
  } else {
	print('The schema is invalid!');
  }
}

nullable_list.dart

import 'package:acanthis/acanthis.dart';

void main() {
  final schema = string().list().nullable();

  final result = schema.tryParse(null);

  if (result.success) {
	print('The schema is valid!');
  } else {
	print('The schema is invalid!');
  }
}

Also you can create lists of nullable types.

import 'package:acanthis/acanthis.dart';

void main() {
  final schema = string().nullable().list();

  final result = schema.tryParse(null);

  if (result.success) {
	print('The schema is valid!');
  } else {
	print('The schema is invalid!');
  }
}

And maps with nullable types.

import 'package:acanthis/acanthis.dart';

void main() {
  final schema = object({
	'name': string().min(3).nullable(),
	'age': number().positive(),
  });

  final result = schema.tryParse({
	'name': null,
	'age': 25,
  });

  if (result.success) {
	print('The schema is valid!');
  } else {
	print('The schema is invalid!');
  }
}