Some sentences in turkish witout subject (hidden subject):

(you/sen) Çarşıya gidecek misin?

(they/onlar) Geldiler mi?

(I/ben) Birazdan yaparım.

(he/she/o) Derslerini yapmış.

I hope it helps

The subject [doer] is not hidden, it is attached to question suffix [mI ] or the verb [-ler]  actually. To me , to call something hidden means there should be no visible sign /trace of that thing .