human
Solve the following python programming problem given the following code:
def server(evt, numrequests) : 
    serv = DocXMLRPCServer (('localhost', 0), logRequests = False) 
    try : 
        global PORT 
        PORT = serv.socket.getsockname () [1] 
        serv.set_server_title ('DocXMLRPCServer Test Documentation') 
        serv.set_server_name ('DocXMLRPCServer Test Docs') 
        serv.set_server_documentation ("This is an XML-RPC server's documentation, but the server can be used by POSTing to /RPC2. Try self.add, too.") 
        class TestClass (object) : 
            def test_method(self, arg) : 
                "Test method's docs. This method truly does very little." 
                self.arg = arg 
serv.register_introspection_functions () 
        serv.register_instance (TestClass ()) 
        def add(x, y) : 
            'Add two instances together. This follows PEP008, but has nothing
            to do with RFC1952. Case should matter: pEp008 and rFC1952.  Things
            that start with http and ftp should be auto-linked, too:
            http://google.com.
            ' 
            return (x + y) 
serv.register_function (PORT) 
        serv.register_function ((lambda x, y : (x - y))) 
        while (numrequests > 0) : 
            serv.handle_request () 
            numrequests -= 1 
except socket.timeout : 
        pass 
finally : 
        serv.server_close () 
        PORT = None 
        evt.set () 

    
    

    Fix the buggy line: serv.register_function (PORT)
assistant
#Here is Python code to fix the buggy line: serv.

serv.register_function (def add()