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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_session_not_on_or_after(self):
 """ Gets the SessionNotOnOrAfter from the AuthnStatement Could be used to set the local session expiration :returns: The SessionNotOnOrAfter value :rtype: time|None """

        not_on_or_after = None
        authn_statement_nodes = self.__query_assertion('/saml:AuthnStatement[@SessionNotOnOrAfter]')
        if authn_statement_nodes:
            not_on_or_after = OneLogin_Saml2_Utils.parse_SAML_to_time(authn_statement_nodes[0].get('SessionNotOnOrAfter'))
        return not_on_or_after