fix(Input, Textarea): keep 0 with the nullable and optional modifiers - #6871

🔗 Linked issue

Resolves #5950

❓ 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)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Input and Textarea mapped empty values with ||=:

if (props.modelModifiers?.nullable) {
  value ||= null
}

||= fires on every falsy value, so combined with the number modifier (or type="number" on Input) a typed 0 went through looseToNumber('0') → 0 and then 0 ||= null → null. .optional had the same problem and produced undefined. Both are the case @sandros94 described in the issue.

??= is not the fix: Input and Textarea must still map '', which ??= would leave untouched. The mapping is now driven by an explicit emptiness test, so '', null and undefined behave exactly as before and only falsy numbers change:

const isEmpty = value === '' || value === null || value === undefined

Select, SelectMenu, InputMenu and Listbox already use ??=, which is right for them — their value is an option, not a typed string — so they are untouched.

Nine table-driven rows added across Input.spec.ts and Textarea.spec.ts, covering both the 0 cases and the '' cases that must not regress. Reverting only the component change turns the five 0 rows red in both the nuxt and vue projects, while the '' rows stay green.

📝 Checklist

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