human
Solve the following python programming problem given the following code:
def ContinueWith(self, fn, on_hub = True) : 
    cw_ar = AsyncResult () 
    def continue_with_callback(_ar) : 
        def run() : 
            try : 
                val = fn (_ar) 
                cw_ar.set (val) 
except : 
                cw_ar.set_exception (sys.exc_info () [1]) 
if on_hub : 
            run () 
else : 
            gevent.spawn (run) 
self.rawlink (<MASK>) 
    return cw_ar 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def continue_with_callback(