nullable

If you use the nullable modifier, given schema will be extended to also match null values, and its output type will be null | T.

const nullableRoleSchema = nullable(oneOf(['User', 'Admin']));
const nullableRoleValidator = validate(nullableRoleSchema);

// Returns 'User', the output type is null | 'User' | 'Admin'
const role = nullableRoleValidator('User');

// Returns null
nullableRoleValidator(null);

// Throws ValidationError
nullableRoleValidator();
nullableRoleValidator(undefined);