[MathiasReichardt]

Summary

Follow-up to #34. Optional arrays blocked Submit, and there was no way to send null for an array.

Arrays

• A nullable array without a default value is sent as null. Before, it was always sent as [].
• A non-nullable array without a default value is required: it gets an asterisk, and Submit stays blocked until it is set.
• The array card shows its state next to the name: null, not set or empty.
  • Removing the last item leaves an empty array.
  • Nullable arrays have a "Set to null" button.
• formly no longer marks arrays as required, because that rejected []. formly's [] default for arrays in required no longer hides a missing value.

Submit

• The Submit tooltip names the invalid fields and the checks that fail, for example Please fix: labels (required).

Layout

• Checkbox fields are as high as text inputs, and the box lines up with input text.
• Array fields keep the same gap to the next field as inputs do.
• The property tree no longer shrinks checkboxes elsewhere in the app. Its ::ng-deep style was not scoped.

Breaking change

A non-nullable array without a default value now blocks Submit until it is set. APIs should send [] as the default value for arrays that may start empty.

Tests

• e2e: nullable and non-nullable arrays (states, request body, "Set to null") and default values from the server.
• Unit: nullability rules for each schema shape, and the list of invalid fields.