fix(select): allow for null/undefined option

[goetzrobin]

currently there is no way to have a null/undefined value as part of our options. we should allow and display the correct option and therefore, we are only resetting the selected options to an empty string and the value to null if there isn't an actual option providing either of them.

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] The commit message follows our guidelines: https://github.com/goetzrobin/spartan/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• [x] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• [x] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, local variables)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Documentation content changes
• [ ] Other... Please describe:

Which package are you modifying?

• [ ] accordion
• [ ] alert
• [ ] alert-dialog
• [ ] aspect-ratio
• [ ] avatar
• [ ] badge
• [ ] button
• [ ] calendar
• [ ] card
• [ ] checkbox
• [ ] collapsible
• [ ] combobox
• [ ] command
• [ ] context-menu
• [ ] data-table
• [ ] date-picker
• [ ] dialog
• [ ] dropdown-menu
• [ ] hover-card
• [ ] icon
• [ ] input
• [ ] label
• [ ] menubar
• [ ] navigation-menu
• [ ] pagination
• [ ] popover
• [ ] progress
• [ ] radio-group
• [ ] scroll-area
• [x] select
• [ ] separator
• [ ] sheet
• [ ] skeleton
• [ ] slider
• [ ] sonner
• [ ] spinner
• [ ] switch
• [ ] table
• [ ] tabs
• [ ] textarea
• [ ] toast
• [ ] toggle
• [ ] tooltip
• [ ] typography

What is the current behavior?

Closes #

What is the new behavior?

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

Other information