redis::cmd.query_async does not work with mobc pool about mobc HOT 3 CLOSED

[dependencies]
tokio = { version = "1.0", features = ["full"]}
redis = { version = "0.19.0", features = ["tokio-comp"] }
mobc = "0.7.0"
mobc-redis = "0.7.0"


use mobc::Pool;
use mobc_redis::redis;
use redis::aio::Connection;
use mobc_redis::RedisConnectionManager;


#[tokio::main]
async fn main() {
    let client = redis::Client::open("redis://127.0.0.1/").unwrap();
    let manager = RedisConnectionManager::new(client);
    let pool = Pool::builder().max_open(20).build(manager);

    let mut conn = pool.get().await.unwrap();
    let s: String = redis::cmd("PING").query_async(&mut conn as &mut Connection).await.unwrap();
    println!("{}", s);
}