rust question

gistfile1.txt

    /// function 1: fine
    pub async fn spawn(self, addr: SocketAddr) -> Result<impl Server, Box<dyn std::error::Error>> {
        let storage = Disk::new(self.path).map_err(Error::from).await?;
        let storage = Verify::new(storage);
        log::info!("Local disk storage initialized.");
    
        Ok(spawn_server(storage, &addr))
    }
    

     /// function 2: fine
    pub async fn spawn(self, addr: SocketAddr) -> Result<impl Server, Box<dyn std::error::Error>> {
        let storage = Disk::new(self.path).map_err(Error::from).await?;
        let storage = Verify::new(Encrypted::new(self.key.unwrap(), storage));
        log::info!("Local disk storage initialized.");
    
        Ok(spawn_server(storage, &addr))
    }
    
    /// function 3: fail with "`if` and `else` have incompatible types"
    pub async fn spawn(self, addr: SocketAddr) -> Result<impl Server, Box<dyn std::error::Error>> {
        let storage = Disk::new(self.path).map_err(Error::from).await?;
        let storage =
            if self.key.is_some() {
                Verify::new(Encrypted::new(self.key.unwrap(), storage))
            } else {
                Verify::new(storage)
            };
        log::info!("Local disk storage initialized.");
    
        Ok(spawn_server(storage, &addr))
    }