def METHOD_NAME(branch, revision):
    route = f"gecko.v2.{branch}.revision.{revision}.taskgraph.decision"
    index = taskcluster_config.get_service("index")
    try:
        return index.findTask(route)["taskId"]
    except taskcluster.exceptions.TaskclusterRestFailure as e:
        if e.status_code == 404:
            return None
        raise