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public/typo3conf/ext/bootstrap_package/Classes/ExpressionLanguage/ConditionProvider.php

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+<?php
+declare(strict_types = 1);
+
+/*
+ * This file is part of the package bk2k/bootstrap-package.
+ *
+ * For the full copyright and license information, please read the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace BK2K\BootstrapPackage\ExpressionLanguage;
+
+use TYPO3\CMS\Core\ExpressionLanguage\AbstractProvider;
+use TYPO3\CMS\Core\Utility\GeneralUtility;
+
+/**
+ * ConditionProvider
+ */
+class ConditionProvider extends AbstractProvider
+{
+    public function __construct()
+    {
+        $this->expressionLanguageVariables = [
+            'extension' => GeneralUtility::makeInstance(ExtensionWrapper::class)
+        ];
+    }
+}

public/typo3conf/ext/bootstrap_package/Classes/ExpressionLanguage/ExtensionWrapper.php

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+<?php
+declare(strict_types = 1);
+
+/*
+ * This file is part of the package bk2k/bootstrap-package.
+ *
+ * For the full copyright and license information, please read the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace BK2K\BootstrapPackage\ExpressionLanguage;
+
+use TYPO3\CMS\Core\Utility\ExtensionManagementUtility;
+
+/**
+ * ExtensionWrapper
+ */
+class ExtensionWrapper
+{
+    /**
+     * @param string $extensionKey
+     * @return bool
+     */
+    public function isLoaded($extensionKey): bool
+    {
+        return ExtensionManagementUtility::isLoaded($extensionKey);
+    }
+}