CreatePullRequestReviewer.
        [Preview API] Add a reviewer to a pull request or cast a vote.
        :param :class:`<IdentityRefWithVote> <azure.devops.v5_1.git.models.IdentityRefWithVote>` reviewer: Reviewer's vote.<br />If the reviewer's ID is included here, it must match the reviewerID parameter.<br />Reviewers can set their own vote with this method.  When adding other reviewers, vote must be set to zero.
        :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 reviewer_id: ID of the reviewer.
        :param str project: Project ID or project name
        :rtype: :class:`<IdentityRefWithVote> <azure.devops.v5_1.git.models.IdentityRefWithVote>`

def create_pull_request_reviewer(self, reviewer, repository_id, pull_request_id, reviewer_id, project=None):
        """CreatePullRequestReviewer.
        [Preview API] Add a reviewer to a pull request or cast a vote.
        :param :class:`<IdentityRefWithVote> <azure.devops.v5_1.git.models.IdentityRefWithVote>` reviewer: Reviewer's vote.<br />If the reviewer's ID is included here, it must match the reviewerID parameter.<br />Reviewers can set their own vote with this method.  When adding other reviewers, vote must be set to zero.
        :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 reviewer_id: ID of the reviewer.
        :param str project: Project ID or project name
        :rtype: :class:`<IdentityRefWithVote> <azure.devops.v5_1.git.models.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')
        if reviewer_id is not None:
            route_values['reviewerId'] = self._serialize.url('reviewer_id', reviewer_id, 'str')
        content = self._serialize.body(reviewer, 'IdentityRefWithVote')
        response = self._send(http_method='PUT',
                              location_id='4b6702c7-aa35-4b89-9c96-b9abf6d3e540',
                              version='5.1-preview.1',
                              route_values=route_values,
                              content=content)
        return self._deserialize('IdentityRefWithVote', response)