Fix date errors for component

[sree-cfa]

Description of change ✍️

• We want "form-group--error" if there is also an overall error for the date field
• cleanup - arrays.isEmpty should also check for null

Priority 🥇

Medium - we can override the component in the meantime

Effect on other applications using FFB 🌊

• TODO verify that this is backwards compatible

✅ Checklist before requesting a review

• Does the new code follow our preferred coding
  style?
• Does the code include javadocs, where necessary?
• Have tests for this feature been added / updated?
• Has the readme been updated?

[enyia21]

Should be an explicit test for the date.html fragment. We should test both the error messages and that the form-group--error class is added appropriately to the group