Add EmptyString support for Formik compatibility

[igorleszczynski]

Add EmptyString support for Formik compatibility

Description

Added support for generating Data Transfer Objects (DTOs) with empty string values instead of null values. This enhancement is particularly useful when working with Formik and Inertia.js in Laravel applications.

Features

• New EmptyStringData trait and interface
• Extended EmptyDataResolver with empty string support
• Static method emptyString() that returns DTO with empty strings as default values

Use Case

When working with Formik forms in React + Inertia.js + Laravel applications, you often need to provide initial values for form fields. Using null values with Formik can cause errors as Formik expects string values for its form fields. Previously, you would need to:

// Before
UserStoreData::empty([
    'name' => '',
    'email' => '',
    'address' => '',
    // ... many more fields
]);

Now you can simply use:

// After
UserStoreData::emptyString();

This is particularly beneficial for large DTOs where manually defining empty values for each field would be tedious and error-prone.
Example with formik, spatie/laravel-typescript-transformer and inertia.js:

Controller:

public function create(): Response
{
    return Inertia::render('Users/UserStorePage', [
        'user' => UserStoreData::form(),
    ]);
}

const UserStorePage: React.FC<{user: UserStoreData}> = ({ user }) => {
    const handleUserStore = (values: UserStoreData, actions: FormikHelpers<UserStoreData>) => {
        /* store method content */
    };

    return <Formik initialValues={user} onSubmit={handleUserStore}>

    </Formik>
};

export default UserStorePage;

Changes

• Added EmptyStringData trait and interface
• Extended EmptyDataResolver with defaultValue parameter
• Updated base Data class to implement EmptyStringData

Breaking Changes

None. This is a backwards-compatible enhancement.

[rrmesquita]

This is a really valid use case. I don't use Formik no more, but React complains as well, when input values transition from undefined to something else, stating that the input went from uncontrolled to controlled.