Error deleting user account as Administrator

I try to delete a user account from the administrator session but I get an error which is described quite well here:
https://www.traccar.org/forums/topic/delete-account/
It says it is fixed but I can't find where the modification was made to fix my code.

this is the error
https://ibb.co/C0Cxvch

I would recommend to upgrade everything, not just this. Then you don't need to search for the change.

Up to version 5.9 I have all the modifications done, I will work on the modifications for version 5.10 and see if that solves it.

Thanks Anton