human
Solve the following python programming problem given the following code:
@ staticmethod 
def adds(arg) : 
    'Mark the method as adding an entity to the collection.

        Adds "add to collection" handling to the method.  The decorator
        argument indicates which method argument holds the SQLAlchemy-relevant
        value.  Arguments can be specified positionally (i.e. integer) or by
        name::

            @collection.adds(1)
            def push(self, item): ...

            @collection.adds(\'entity\')
            def do_stuff(self, thing, entity=None): ...

        ' 
    def decorator(fn) : 
        fn._sa_instrument_before = ('fire_append_event', arg) 
        return fn 
return arg 

    
    

    Fix the buggy line: return arg
assistant
#Here is Python code to fix the buggy line: return arg
.

return def decorator(