def create_pull_request_reviewers(self, reviewers, repository_id, pull_request_id, project=None):
        """CreatePullRequestReviewers.
        [Preview API] Add reviewers to a pull request.
        :param [IdentityRef] reviewers: Reviewers to add to the pull request.
        :param str repository_id: The repository ID of the pull request’s target branch.
        :param int pull_request_id: ID of the pull request.
        :param str project: Project ID or project name
        :rtype: [IdentityRefWithVote]
        """
        route_values = {}
        if project is not None:
            route_values['project'] = self._serialize.url('project', project, 'str')
        if repository_id is not None:
            route_values['repositoryId'] = self._serialize.url('repository_id', repository_id, 'str')
        if pull_request_id is not None:
            route_values['pullRequestId'] = self._serialize.url('pull_request_id', pull_request_id, 'int')
        content = self._serialize.body(reviewers, '[IdentityRef]')
        response = self._send(http_method='POST',
                              location_id='4b6702c7-aa35-4b89-9c96-b9abf6d3e540',
                              version='5.1-preview.1',
                              route_values=route_values,
                              content=content)
        return self._deserialize('[IdentityRefWithVote]', self._unwrap_collection(response))