[FOLLOWUP][!!!][TASK] Split service class of Import/Export (impexp)

Restore change that was reverted by accident.

Releases: master
Resolves: #72710
Change-Id: Iaeb622f89c69eb435bed79c60a18052e419dca28
Reviewed-on: https://review.typo3.org/45974


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>

typo3/sysext/impexp/Classes/ImportExport.php

@@ -289,7 +289,7 @@ abstract class ImportExport
         // Check extension dependencies:
         if (is_array($this->dat['header']['extensionDependencies'])) {
             foreach ($this->dat['header']['extensionDependencies'] as $extKey) {
-                if (!ExtensionManagementUtility::isLoaded($extKey)) {
+                if (!empty($extKey) && !ExtensionManagementUtility::isLoaded($extKey)) {
                     $this->error('DEPENDENCY: The extension with key "' . $extKey . '" must be installed!');
                 }
             }