--- ./vendor/magento/module-catalog-import-export/Model/Import/Product/CategoryProcessor.php	2022-09-08 14:59:29.173882515 +0000
+++ ./vendor/magento/module-catalog-import-export/Model/Import/Product/CategoryProcessor.php	2022-09-08 14:28:44.345000000 +0000
@@ -252,7 +252,7 @@
      */
     private function quoteDelimiter($string)
     {
-        return str_replace(self::DELIMITER_CATEGORY, '\\' . self::DELIMITER_CATEGORY, $string);
+        return str_replace(self::DELIMITER_CATEGORY, '\\' . self::DELIMITER_CATEGORY, $string ?? '');
     }

     /**
@@ -263,6 +263,6 @@
      */
     private function unquoteDelimiter($string)
     {
-        return str_replace('\\' . self::DELIMITER_CATEGORY, self::DELIMITER_CATEGORY, $string);
+        return str_replace('\\' . self::DELIMITER_CATEGORY, self::DELIMITER_CATEGORY, $string ?? '');
     }
 }