[Experiment] Fix additional address field validation notices (#44615)

plugins/woocommerce-blocks/assets/js/base/components/combobox/style.scss

@@ -104,6 +104,12 @@
 					}
 				}
 
+				// Force empty rows to have a height.
+				&::after {
+					content: " ";
+					display: inline-block;
+				}
+
 				&:hover,
 				&:focus,
 				&.is-highlighted,

plugins/woocommerce/changelog/add-register-checkout-field-show-in-options-43524

@@ -1,4 +1,4 @@
 Significance: patch
 Type: update
 
-This is behind a feature flag.
+Comment: This is behind a feature flag

plugins/woocommerce/changelog/fix-additional-address-field-validation-notices

@@ -0,0 +1,4 @@
+Significance: patch
+Type: update
+
+This is behind a feature flag.

plugins/woocommerce/src/Blocks/Domain/Services/CheckoutFields.php

@@ -257,7 +257,7 @@ public function add_session_meta_keys( $keys ) {
 	 * @return mixed
 	 */
 	public function default_sanitize_callback( $value, $field ) {
-		return wc_clean( $value );
+		return $value;
 	}
 
 	/**
@@ -433,13 +433,6 @@ private function process_select_field( $field_data, $options ) {
 			return false;
 		}
 
-		// Select fields are always required. Log a warning if it's set explicitly as false.
-		$field_data['required'] = true;
-		if ( isset( $options['required'] ) && false === $options['required'] ) {
-			$message = sprintf( 'Registering select fields as optional is not supported. "%s" will be registered as required.', $id );
-			_doing_it_wrong( 'woocommerce_blocks_register_checkout_field', esc_html( $message ), '8.6.0' );
-		}
-
 		$cleaned_options = array();
 		$added_values    = array();
 
@@ -469,6 +462,20 @@ private function process_select_field( $field_data, $options ) {
 		}
 
 		$field_data['options'] = $cleaned_options;
+
+		// If the field is not required, inject an empty option at the start.
+		if ( isset( $field_data['required'] ) && false === $field_data['required'] && ! in_array( '', $added_values, true ) ) {
+			$field_data['options'] = array_merge(
+				array(
+					array(
+						'value' => '',
+						'label' => '',
+					),
+				),
+				$field_data['options']
+			);
+		}
+
 		return $field_data;
 	}