def galprop_sourcekey(self, **kwargs):
        """ return the sourcekey for merged galprop maps :
        specifies the merged component and merging scheme
        """
        kwargs_copy = self.base_dict.copy()
        kwargs_copy.update(**kwargs)
        self._replace_none(kwargs_copy)        
        try:
            return NameFactory.galprop_sourcekey_format.format(**kwargs_copy)
        except KeyError:
            return None
return the sourcekey for merged galprop maps :
        specifies the merged component and merging scheme