--- a/vendor/magento/module-customer/Block/Address/Edit.php
+++ b/vendor/magento/module-customer/Block/Address/Edit.php
@@ -125,7 +125,7 @@
         if ($postedData = $this->_customerSession->getAddressFormData(true)) {
             $postedData['region'] = [
                 'region_id' => isset($postedData['region_id']) ? $postedData['region_id'] : null,
-                'region' => $postedData['region'],
+                'region' => $postedData['region'] ?? null,
             ];
             $this->dataObjectHelper->populateWithArray(
                 $this->_address,