ListUsers.
        [Preview API] Get a list of all users in a given scope.
        :param [str] subject_types: A comma separated list of user subject subtypes to reduce the retrieved results, e.g. msa’, ‘aad’, ‘svc’ (service identity), ‘imp’ (imported identity), etc.
        :param str continuation_token: An opaque data blob that allows the next page of data to resume immediately after where the previous page ended. The only reliable way to know if there is more data left is the presence of a continuation token.
        :rtype: :class:`<PagedGraphUsers> <azure.devops.v5_1.graph.models.PagedGraphUsers>`

def list_users(self, subject_types=None, continuation_token=None):
        """ListUsers.
        [Preview API] Get a list of all users in a given scope.
        :param [str] subject_types: A comma separated list of user subject subtypes to reduce the retrieved results, e.g. msa’, ‘aad’, ‘svc’ (service identity), ‘imp’ (imported identity), etc.
        :param str continuation_token: An opaque data blob that allows the next page of data to resume immediately after where the previous page ended. The only reliable way to know if there is more data left is the presence of a continuation token.
        :rtype: :class:`<PagedGraphUsers> <azure.devops.v5_1.graph.models.PagedGraphUsers>`
        """
        query_parameters = {}
        if subject_types is not None:
            subject_types = ",".join(subject_types)
            query_parameters['subjectTypes'] = self._serialize.query('subject_types', subject_types, 'str')
        if continuation_token is not None:
            query_parameters['continuationToken'] = self._serialize.query('continuation_token', continuation_token, 'str')
        response = self._send(http_method='GET',
                              location_id='005e26ec-6b77-4e4f-a986-b3827bf241f5',
                              version='5.1-preview.1',
                              query_parameters=query_parameters)
        response_object = models.PagedGraphUsers()
        response_object.graph_users = self._deserialize('[GraphUser]', self._unwrap_collection(response))
        response_object.continuation_token = response.headers.get('X-MS-ContinuationToken')
        return response_object