Issue #6924: Unmask exception message during product import

Probably a typo. Exception message was passed as a exception description argument instead of exception message. Artefact of optional parameters.

Author: tim-bezhashvyly

app/code/Magento/ImportExport/Model/Import.php

@@ -567,7 +567,6 @@ public function validateSource(\Magento\ImportExport\Model\Import\AbstractSource
                 ProcessingError::ERROR_LEVEL_CRITICAL,
                 null,
                 null,
-                null,
                 $e->getMessage()
             );
         }