@Override
    public <T> Mono<T> findOne(Class<T> clazz, Filter filter, @Nullable QueryOptions options) {
        MongoCollection<T> collection = context.getCollection(clazz);
        options = options == null
                ? QueryOptions.newBuilder(1)
                        .limit(1)
                : options.limit(1);
        FindPublisher<T> source = find(collection, filter, options);
        return Mono.from(source);
    }
@author James Chen
@implNote 1. We operate in an unsafe way, which means we don't check whether arguments are legal
          or not and so on 2. The publishers of mongo-java-driver are cold and the publishers of
          TurmsMongoOperations are also cold Reference:
          https://github.com/mongodb/mongo/blob/master/src/mongo/shell/utils_sh.js
turms-server-common/src/main/java/im/turms/server/common/storage/mongo/operation/TurmsMongoOperations.java