def get_function_vault_assignment_session(self, proxy=None):
if proxy is None:<EOL><INDENT>raise NullArgument()<EOL><DEDENT>raise Unimplemented()<EOL>
Gets the session for assigning function to vault mappings.

        arg:    proxy (osid.proxy.Proxy): a proxy
        return: (osid.authorization.FunctionVaultAssignmentSession) - a
                ``FunctionVaultAssignmentSession``
        raise:  NullArgument - ``proxy`` is ``null``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - ``supports_function_vault_assignment()``
                is ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_function_vault_assignment()`` is ``true``.*