Cannot specialize non-generic type 'DefaultsKey'

[Qu000]

import SwiftyUserDefaults

// MARK: 定义key
extension DefaultsKeys {
/// 用户Token
var RRUserToken: DefaultsKey<String?> { .init("RRUserToken", defaultValue: "") }
}

就直接报错 Cannot specialize non-generic type 'DefaultsKey' 了，为啥啊....