human
Solve the following python programming problem given the following code:
def add_bgp_error_metadata(code, sub_code, def_desc = 'unknown') : 
    'Decorator for all exceptions that want to set exception class meta-data.
    ' 
    if (_EXCEPTION_REGISTRY.get ((code, sub_code)) is not None) : 
        raise ValueError (('BGPSException with code %d and sub-code %d already defined.' % (code, sub_code))) 
def decorator(klass) : 
        'Sets class constants for exception code and sub-code.

        If given class is sub-class of BGPSException we sets class constants.
        ' 
        if issubclass (klass, BGPSException) : 
            _EXCEPTION_REGISTRY [(code, sub_code)] = klass 
            klass.CODE = code 
            klass.SUB_CODE = sub_code 
            klass.DEF_DESC = def_desc 
return klass 
return sub_code 

    
    

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

return def decorator(