Steps to reproduce:

1. Authenticate to the API as a user with "Super admin role"
2. Try to change another users password through the API with the current_password parameter set to the empty string.

Result:

Observe that a blank current_passwd isn't allowed. You must know the current password.

Expected:

It should be possible to have the parameter blank, like stated in the docs:
https://www.zabbix.com/documentation/6.4/en/manual/api/reference/user/update