This PR …

• We cannot simply add an empty string as fallback here https://github.com/getkirby/kirby/pull/5076/files#diff-04e8dc6763a997696e500ceeb03a7f770ea1c14df821298111e13dbecaaeef5eR12 - this will screw with all fields that don't expect a string as value prop (e.g. blocks). They rely on undefined to have their prop default kick in.
• Instead we check in the inVisible helper if the when condition is set to an empty string that undefined will be just as fine

Fixes

• Fix displaying conditional fields for empty when condition
  Select field has no initial value in structure/object fields #4838

Enhancements

• New $helper.field.form(fields) function to set up values for an empty form

Ready?

• Unit tests for fixed bug/feature
• In-code documentation (wherever needed)
• Tests and checks all pass

For review team

• Add changes to release notes draft in Notion
• Add to website docs release checklist (if needed)