Hi Mohamed,
It does not make sense to me why you would want to have the affected end user not to be required. Do you not have the need to use this field at all? Can you give us the complete business case?
If you don't anticipate to use this field at all, one workaround is to by pass this is to hide the field on the form. Then create a dummy user in the contact table and then create a defaulting data-partition so that when a ticket is created this field is set to that dummy user. this way the ticket will be created without you having to manually fill in this user.
Kind Regards,
Brian