«فإذا لم يذكر معه فالغرض إن كان إثباته لفاعله أو نفيه عنه مطلقا، نزل منزلة اللازم، ولم يقدر له مفعول؛ لأن المقدر كالمذكور»
When omission serves to affirm or deny an action of its agent absolutely, the verb is treated like an intransitive one; no object is assumed, because an implied object would limit the meaning just as an expressed one does.
The point of absolute affirmation or denial is to focus on whether the action characterizes its subject, without restricting the statement to an object. Supplying a hidden noun automatically would undo that rhetorical choice.
Accordingly, the grammatical possibility that a verb takes an object does not require the rhetorician to invent one in every occurrence.