[BUGFIX] Let Country object retrieval handle NULL value

This fixes a PHP type error when saving a NULL value as
country object.

Can be reproduced by saving an EXT:styleguide entry of type
"elements - select" with default values (only fill in required
fields).

Resolves: #107094
Releases: main
Change-Id: I861f94399ec7d2a6ca329a65290991e81798b2bd
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/90059
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Sebastian Iffland <sebastian.iffland@fullhaus.de>
Reviewed-by: Garvin Hicking <garvin@hick.ing>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Tested-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Garvin Hicking <garvin@hick.ing>

Author: garvinhicking

typo3/sysext/backend/Classes/Utility/BackendUtility.php

@@ -1693,7 +1693,7 @@ public static function getProcessedValue(
                 }
                 break;
             case 'country':
-                $country = GeneralUtility::makeInstance(CountryProvider::class)->getByIsoCode($value);
+                $country = GeneralUtility::makeInstance(CountryProvider::class)->getByIsoCode($value ?? '');
                 if ($country) {
                     $l = $lang->sL($country->getLocalizedNameLabel());
                 }

typo3/sysext/core/Classes/Country/CountryProvider.php

@@ -1743,6 +1743,11 @@ public function getAll(): array
         return $this->countries;
     }
 
+    /**
+     * Searches for a matching country with fallback; uses Alpha2 ISO-Code by
+     * default, and if that does not match, compare the input $isoCode
+     * as an Alpha3 ISO-Code.
+     */
     public function getByIsoCode(string $isoCode): ?Country
     {
         $isoCode = strtoupper($isoCode);
@@ -1773,6 +1778,7 @@ public function getByAlpha3IsoCode(string $isoCode): ?Country
         }
         return null;
     }
+
     public function getByEnglishName(string $name): ?Country
     {
         foreach ($this->countries as $country) {

typo3/sysext/core/Tests/Unit/Country/CountryProviderTest.php

@@ -47,6 +47,14 @@ public function findByIsoCodeReturnsValidObject(): void
         self::assertEquals('French Republic', $countryIsoCode2->getOfficialName());
     }
 
+    #[Test]
+    public function findByUnspecifiedIsoCodeReturnsNull(): void
+    {
+        $subject = new CountryProvider(new NoopEventDispatcher());
+        $emptyIsocode = $subject->getByIsoCode('');
+        self::assertNull($emptyIsocode);
+    }
+
     #[Test]
     public function findByThreeLetterIsoCodeReturnsValidObject(): void
     {

typo3/sysext/form/Classes/ViewHelpers/RenderFormValueViewHelper.php

@@ -99,7 +99,7 @@ protected function processElementValue(
         $properties = $element->getProperties();
         $options = $properties['options'] ?? null;
         if ($element->getType() === 'CountrySelect') {
-            $country = GeneralUtility::makeInstance(CountryProvider::class)->getByIsoCode($value);
+            $country = GeneralUtility::makeInstance(CountryProvider::class)->getByIsoCode($value ?? '');
             if ($country !== null) {
                 return $country->getName();
             }