human
Solve the following python programming problem given the following code:
@ staticmethod 
def register_of_version(version) : 
    def _register_of_version(cls) : 
        OfCtl._OF_VERSIONS.setdefault (version, cls) 
        return cls 
return <MASK> 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def _register_of_version(