GetClassificationNodes.
        [Preview API] Gets root classification nodes or list of classification nodes for a given list of nodes ids, for a given project. In case ids parameter is supplied you will  get list of classification nodes for those ids. Otherwise you will get root classification nodes for this project.
        :param str project: Project ID or project name
        :param [int] ids: Comma seperated integer classification nodes ids. It's not required, if you want root nodes.
        :param int depth: Depth of children to fetch.
        :param str error_policy: Flag to handle errors in getting some nodes. Possible options are Fail and Omit.
        :rtype: [WorkItemClassificationNode]

def get_classification_nodes(self, project, ids, depth=None, error_policy=None):
        """GetClassificationNodes.
        [Preview API] Gets root classification nodes or list of classification nodes for a given list of nodes ids, for a given project. In case ids parameter is supplied you will  get list of classification nodes for those ids. Otherwise you will get root classification nodes for this project.
        :param str project: Project ID or project name
        :param [int] ids: Comma seperated integer classification nodes ids. It's not required, if you want root nodes.
        :param int depth: Depth of children to fetch.
        :param str error_policy: Flag to handle errors in getting some nodes. Possible options are Fail and Omit.
        :rtype: [WorkItemClassificationNode]
        """
        route_values = {}
        if project is not None:
            route_values['project'] = self._serialize.url('project', project, 'str')
        query_parameters = {}
        if ids is not None:
            ids = ",".join(map(str, ids))
            query_parameters['ids'] = self._serialize.query('ids', ids, 'str')
        if depth is not None:
            query_parameters['$depth'] = self._serialize.query('depth', depth, 'int')
        if error_policy is not None:
            query_parameters['errorPolicy'] = self._serialize.query('error_policy', error_policy, 'str')
        response = self._send(http_method='GET',
                              location_id='a70579d1-f53a-48ee-a5be-7be8659023b9',
                              version='5.1-preview.2',
                              route_values=route_values,
                              query_parameters=query_parameters)
        return self._deserialize('[WorkItemClassificationNode]', self._unwrap_collection(response))