use `undefined` instead of `null` for empty `form` prop

Describe the problem

Using the new actions feature of SvelteKit, when loading the page the form prop is set to null. In my usecase I return an errors object if some of the form fields don’t pass the validation in the action.

To not having to deal with unnecessary if checks or optional chainings, I’m setting errors to an empty object when the page loads and form is still null.

<script>
	export let form
	$: ({ errors } = form || { errors: { } }
</script>

{#if errors.email}
	invalid email address
{/if}

{#if form.errors.password} <!-- Uncaught TypeError: Cannot read properties of null (reading 'errors') -->
	please enter a stronger password
{/if}

This works fine, if I only use the errors object in that file. But if I accidentially access form again, I’ll get an error because form is still null.

To not having the issue above I would need to set the default value like this:

<script>
	export let form
	$: form = form || { errors: { } }
</script>

But this requires me to write additional code.

Describe the proposed solution

form should be undefined and not null to make it possible to set a fallback value like you would do in other Svelte components:

<script>
	export let form = { errors: { } }
	$: ({ errors } = form
</script>

{#if errors.email}
	invalid email address
{/if}

{#if form.errors.password} <!-- no error! -->
	please enter a stronger password
{/if}

Alternatives considered

Leave it as it is.

Importance

would make my life easier

Additional Information

No response

[Tal500]

You may use the relatively new JS/TS language feature “?”: form?.errors?.blabla

Every “?.*” junction will return undefined if the l.h.s. is undefined or null, and the original value otherwise.

[ivanhofer]

I think this conversation is moving in a different direction.

My initial suggestion was to just use undefined instead of null to be able to set an initial default value when the page loads. With undefined we could use the same concept as for regular Svelte components. Once a form gets submitted the developer is responsible for returning a useful value or to handle cases where nothing gets returned.