如何将RSA私钥转换为pem

我需要将使用RsaPrivateKey::new()生成的私钥转换为pem,但无法通过文档了解如何执行此操作

use rsa::{PublicKey, RsaPrivateKey, RsaPublicKey, PaddingScheme, pkcs8::EncodePrivateKey};

// create a private key
let mut rng = rand::thread_rng();
let bits = 2048;
let private_key = RsaPrivateKey::new(&mut rng, bits).expect("Failed to generate key");
// create a public key / address
let public_key = RsaPublicKey::from(&private_key);

创建pem时会返回一个错误,表示LineEnding未声明,但文档中就是这样做的:

let priv_pem = RsaPrivateKey::to_pkcs8_pem(&private_key, line_ending: LineEnding::default);