rails how to reject updating when a parameter is missing

i'm kind of new to rails and i want to require a user to input his current_password before updating his infos. I know this can be achieved through devise but i want to do it without devise because i'm having a really hard time modifying the devise.

what i have in mind is something like this:

def update

        @edi_user = EdiUser.find(@trader_edi_user.edi_user_id)
        @edi_user.update_attributes(edi_user_params.reject_if{ |attr| params['current_password'].blank? })

        redirect_to :back
    end

i know this code is wrong, but is this kind of logic possible in rails?

Or can anybody help me how to code the right syntax?

thank you in advance