[BUGFIX] Always return a string for PHP 8.1

The following deprecation occurred in PHP 8.1:
PHP Runtime Deprecation Notice: trim(): Passing null to parameter #1 ($string) of type string is deprecated.

This happens in various places:
* Using stdWrap_field() or in stdWrap() places
* BackendUtility (e.g. new IRRE elements)
* ExtensionManager

Resolves: #96354
Releases: main, 11.5
Change-Id: Ie5c721784b51ed5493c8d9e1d557b08611263f6b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72659
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>

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

@@ -629,12 +629,16 @@ public static function getTCAtypeValue($table, $row)
             $field = $GLOBALS['TCA'][$table]['ctrl']['type'] ?? '';
             if (str_contains($field, ':')) {
                 [$pointerField, $foreignTableTypeField] = explode(':', $field);
-                // Get field value from database if field is not in the $row array
-                if (!isset($row[$pointerField])) {
-                    $localRow = self::getRecord($table, $row['uid'], $pointerField);
-                    $foreignUid = $localRow[$pointerField];
-                } else {
-                    $foreignUid = $row[$pointerField];
+                // Check if the record has been persisted already
+                $foreignUid = 0;
+                if (isset($row['uid'])) {
+                    // Get field value from database if field is not in the $row array
+                    if (!isset($row[$pointerField])) {
+                        $localRow = self::getRecord($table, $row['uid'], $pointerField);
+                        $foreignUid = $localRow[$pointerField];
+                    } else {
+                        $foreignUid = $row[$pointerField];
+                    }
                 }
                 if ($foreignUid) {
                     $fieldConfig = $GLOBALS['TCA'][$table]['columns'][$pointerField]['config'];

typo3/sysext/core/Classes/Package/Package.php

@@ -138,11 +138,11 @@ protected function loadFlagsFromComposerManifest()
     protected function createPackageMetaData(PackageManager $packageManager)
     {
         $this->packageMetaData = new MetaData($this->getPackageKey());
-        $description = $this->getValueFromComposerManifest('description');
+        $description = (string)$this->getValueFromComposerManifest('description');
         $this->packageMetaData->setDescription($description);
         $this->packageMetaData->setTitle($this->getValueFromComposerManifest('title') ?? $description);
-        $this->packageMetaData->setVersion($this->getValueFromComposerManifest('version'));
-        $this->packageMetaData->setPackageType($this->getValueFromComposerManifest('type'));
+        $this->packageMetaData->setVersion((string)$this->getValueFromComposerManifest('version'));
+        $this->packageMetaData->setPackageType((string)$this->getValueFromComposerManifest('type'));
         $requirements = $this->getValueFromComposerManifest('require');
         if ($requirements !== null) {
             foreach ($requirements as $requirement => $version) {

typo3/sysext/frontend/Classes/ContentObject/ContentObjectRenderer.php

@@ -1287,7 +1287,7 @@ public function stdWrap($content = '', $conf = [])
         unset($this->stopRendering[$this->stdWrapRecursionLevel]);
         $this->stdWrapRecursionLevel--;
 
-        return $content;
+        return (string)$content;
     }
 
     /**
@@ -1443,7 +1443,7 @@ public function stdWrap_data($_ = '', $conf = [])
      */
     public function stdWrap_field($content = '', $conf = [])
     {
-        return $this->getFieldVal($conf['field']);
+        return (string)$this->getFieldVal($conf['field']);
     }
 
     /**
@@ -5784,8 +5784,8 @@ public function getQuery($table, $conf, $returnQueryArray = false)
         foreach ($properties as $property) {
             $conf[$property] = trim(
                 isset($conf[$property . '.'])
-                    ? $this->stdWrap($conf[$property] ?? '', $conf[$property . '.'] ?? [])
-                    : ($conf[$property] ?? '')
+                    ? (string)$this->stdWrap($conf[$property] ?? '', $conf[$property . '.'] ?? [])
+                    : (string)($conf[$property] ?? '')
             );
             if ($conf[$property] === '') {
                 unset($conf[$property]);