fix(nuxt): allow cookies to be set to null to unset them

[danielroe]

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

remake of #8754

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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[Aareksio]

@danielroe This caused useCookie<Type[]>('name', { default: () => [] }) to be Ref<Type[] | null> which forces us to write null checks while in reality the type is strictly never null.

[danielroe]

@Aareksio I appreciate it; the issue is that it can be null if you set it to null. You could cast it as Ref<Type[]> in your case.

[Aareksio]

After this change, all code must be explicitly null-checked or as-patched.
I would argue that neither of the following is good DX:

const languages = useCookie<string[]>('languages', { default: () => ['en'] }) as Ref<string[]>
// or
for (const language of (languages as Ref<string[]>).value) {}

---

I understand the reasoning on why the change was made. It just seems to break more (important) use-cases than it fixes.

[danielroe]

I wonder if we could allow overriding with generic - so by default it infers a type with null, but you can override by setting your own value? And if you need to delete you can add | null to the generic type?

[Aareksio]

Before the change, you should be able to do useCookie<string | null>() and the type would be Ref<string | null>. Rather painless opt-in.

---

https://github.com/nuxt/framework/blob/main/packages/nuxt/src/app/composables/cookie.ts#L26
Here it could be T = string | null as default, allowing for easy manual override if necessary.