jsonデータの取得

import Foundation 
import CryptoSwift 

struct JsonSample : Codable {
    var high : Double
    var open : Double
    var bid : Double
    var currencyPairCode : String
    var ask : Double
    var low: Double 
} 

let listUrl = "https://www.gaitameonline.com/rateaj/getrate"

let url = URL(string: listUrl)

URLSession.shared.dataTask(with: url) { (data, response, error) in
    if error != nil {
        print(error!.localizedDescription)
    }

    guard let data = data else { return }

    let json = try? JSONDecoder().decode([JsonSample].self, from: data)
    
}.resume()
print(json.bid)

エラーになる。何故だ。。。
/tmp/EA9CF30B-2A75-422F-B05F-493561545E26.sMmRoI/main.swift:19:34: error: value of optional type ‘URL?’ not unwrapped; did you mean to use ‘!’ or ‘?’?
URLSession.shared.dataTask(with: url) { (data, response, error) in
^
!
/tmp/EA9CF30B-2A75-422F-B05F-493561545E26.sMmRoI/main.swift:29:7: error: use of unresolved identifier ‘json’
print(json.bid)

なんかうまくいかない。

let url:URL = URL(string: "")!
let task = URLSession.shared.dataTask(with: url){ data, response, error in
	if let error = error{
		print(error.localizedDescription)
		return
	}
	if let response = response as? HTTPURLResponse {
		print("response.statusCode = \(response.statusCode)")
	}
}
task.resume()