As the object of active voice becomes the subject of passive voice and the subject of active voice comes after preposition by.(and sometimes dropped) I dont think there is an object there. Right?
It rather depends on how you parse the passive voice. The verb that really tells you what it means, together with any indirect object of that verb, could be thought of as the object, and the "object" of that verb as the subject - and the verb is "to be".
If you think of the passivised verb as the principle verb, then there an object but no subject.