Look up the name of a module by LSID assigned by the authority.
        Returns None if the LSID is not found.
        :param lsid:
        :return: string or none

def lookup(self, lsid):
        """
        Look up the name of a module by LSID assigned by the authority.
        Returns None if the LSID is not found.
        :param lsid:
        :return: string or none
        """
        if self.registered_modules is None or lsid not in self.registered_modules:
            return None
        else:
            return self.registered_modules[lsid]