handle empty id tag in stopTransaction

[HMNoureldin]

• according to OCTT , TestCase 032_2 when the powerless occurred while the vehicle is charging and you don't have a backup power source then the charging point should send stop transaction to the back-end to close the opened session when powerless happened , but in this case the charging-point doesn't have the id-tag that corresponds to that opened session as we keep it as part of the session in the run time , so the only way to stop the session is to get this id-tag from the cache data base.

@mahdidadashi65 @thom-gh @SiarheiVolkau @ruudvd

[c-jimenez]

Hi,
I'm not sure you have to send an idTag in this case since no user has presented physically nor remotely an idTag to stop the transaction.
The StopReason::PowerLoss should be sufficient.