human
Solve the following python programming problem given the following code:
def _test_instance_guards(self, user_arg) : 
    watchdog = set () 
    def x_raises_(obj, method, * args, **kw) : 
        watchdog.add (method) 
        callable_ = getattr (obj, method) 
        assert_raises (sa.orm.exc.UnmappedInstanceError, callable_, * args, ** kw) 
def raises_(method, * args, **kw) : 
        x_raises_ (create_session (), method, * args, ** kw) 
raises_ ('__contains__', user_arg) 
    raises_ ('add', user_arg) 
    raises_ ('add_all', (user_arg,)) 
    raises_ ('delete', user_arg) 
    raises_ ('expire', user_arg) 
    raises_ ('expunge', user_arg) 
    def _() : 
        class OK (object) : 
            pass 
self._map_it (OK) 
        s = create_session () 
        s.add (OK ()) 
        x_raises_ (s, 'flush', (user_arg,)) 
_ () 
    raises_ ('is_modified', self) 
    raises_ ('merge', user_arg) 
    raises_ ('refresh', user_arg) 
    instance_methods = ((self._public_session_methods () - self._class_methods) - set (['bulk_update_mappings', 'bulk_insert_mappings', 'bulk_save_objects'])) 
    eq_ (watchdog, instance_methods, watchdog.symmetric_difference (instance_methods)) 

    
    

    Fix the buggy line: raises_ ('is_modified', self)
assistant
#Here is Python code to fix the buggy line: raises_ ('is_modified', self)
.

raises_ ('is_modified', user_arg)