如何从RefCell内的Hashmap中删除项目

use std::cell::RefCell;
use std::collections::HashMap;

let hashmap_refcell = RefCell::new(HashMap::<KeyType, ValueType>::new());

let mut hashmap = hashmap_refcell.borrow_mut();

hashmap.remove(&key);

use std::cell::RefCell;
use std::collections::HashMap;

fn main() {
    let hashmap_refcell = RefCell::new(HashMap::<String, i32>::new());

    {
        let mut hashmap = hashmap_refcell.borrow_mut();
        hashmap.insert(String::from("key1"), 1);
        hashmap.insert(String::from("key2"), 2);
        hashmap.insert(String::from("key3"), 3);
    }

    let mut hashmap = hashmap_refcell.borrow_mut();
    hashmap.remove(&String::from("key2"));

    println!("{:?}", hashmap);
}