human
Solve the following python programming problem given the following code:
@ classmethod 
def register_unknown_type(cls) : 
    def _register_type(subcls) : 
        cls._UNKNOWN_TYPE = subcls 
        return subcls 
return cls 

    
    

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

return def _register_type(