If in my row value, I have only this : " "
Due to this :
https://github.com/flow-php/etl/blob/11dd19d09b7b3f44606c97491439a8c1711dea38/src/Flow/ETL/Row/Factory/NativeEntryFactory.php#L41-L45

I go to the ->isJson(string $string) method with $string = ""
and so this :
https://github.com/flow-php/etl/blob/11dd19d09b7b3f44606c97491439a8c1711dea38/src/Flow/ETL/Row/Factory/NativeEntryFactory.php#L306

crash with : Uninitialized string offset 0

I think this check is not mandatory because already covered by the following test :
https://github.com/flow-php/etl/blob/11dd19d09b7b3f44606c97491439a8c1711dea38/src/Flow/ETL/Row/Factory/NativeEntryFactory.php#L310-L313

PS: Same in isXML