human
Solve the following python programming problem given the following code:
def add_button(self, label, cb, * userdata) : 
    bn = gtk.Button (label) 
    bn.set_property ('can-focus', False) 
    self._hbox2.pack_start (self._mka (on_click), False, False, 2) 
    def on_click(* args) : 
        cb (* userdata) 
        self._after_button_pressed.fire () 
bn.connect ('clicked', on_click) 

    
    

    Fix the buggy line: self._hbox2.pack_start (self._mka (on_click), False, False, 2)
assistant
#Here is Python program to fix the buggy line: self.

self._hbox2.pack_start (self._mka (bn), False, False, 2)