Unexpected nil in JSON strings

Question

I parse JSON in my application and some of the JSONs have nil values which I handled. However, the app still shows me the error that JSON contains nil values. My code:

struct Response : Decodable {
let articles: [Article]
 }

struct Article: Decodable {

let title: String
let description : String
let url : String
let urlToImage : String
}
URLSession.shared.dataTask(with: url) { (data, response, error) in
     guard let data = data else { return }
     do {
     let article =  try JSONDecoder().decode(Response.self , from : data)
     for i in 0...article.articles.count - 1 {
         if type(of: article.articles[i].title) == NSNull.self {
             beforeLoadNewsViewController.titleArray.append("")
         } else {
             beforeLoadNewsViewController.titleArray.append(article.articles[i].title)
         }
if type(of : article.articles[i].urlToImage) == NSNull.self {
                beforeLoadNewsViewController.newsImages.append(newsListViewController.newsImages[newsListViewController.newsIndex])

                    } else {
                        
                        
                    let url = URL(string: article.articles[i].urlToImage ?? "https://static.wixstatic.com/media/b77fe464cfc445da9003a5383a3e1acf.jpg")
                    
                        
                    let data = try? Data(contentsOf: url!)

                    if url != nil {

                    //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
                        let img = UIImage(data: data!)
                    beforeLoadNewsViewController.newsImages.append(img!)

                    } else {
                beforeLoadNewsViewController.newsImages.append(newsListViewController.newsImages[newsListViewController.newsIndex])

                        }

This is the error running the app:

FC91DEECC1631350EFA71C9C561D).description], debugDescription: "Expected String value but found null instead.", underlyingError: nil))

Note:

This JSON works with other urls that don't have nil values.

and here is the json

{
    "status": "ok",
    "source": "entertainment-weekly",
    "sortBy": "top",
    "articles": [
    {
        "author": null,
        "title": "Hollywood's Original Gone Girl",
        "description": null,
        "url": "http://mariemcdonald.ew.com/",
        "urlToImage": null,
        "publishedAt": null
    },
    {
        "author": "Samantha Highfill",
        "title": "‘Supernatural’: Jensen Ackles, Jared Padalecki say the boys aren’t going ‘full-mope’",
        "description": "",
        "url": "http://ew.com/tv/2017/10/18/supernatural-jensen-ackles-jared-padalecki-season-13/",
        "urlToImage": "http://ewedit.files.wordpress.com/2017/10/supernatural-season-13-episode-1.jpg?crop=0px%2C0px%2C2700px%2C1417.5px&resize=1200%2C630",
        "publishedAt": "2017-10-18T17:23:54Z"
    },
    {

The JSON you’re trying to decide which returns this error... — jcaron, Oct 17 '17 at 16:51
ok I added this and edited my question so you can see null values in json — Saeed Rahmatolahi, Oct 18 '17 at 17:55
Can you provide the definitions for the various types (classes) you're using? You're apparently not allowing null values for one of the properties of articles. — jcaron, Oct 18 '17 at 23:27
apart from nullable values, another stupid reason for having that error could be simply getting malformed json (or 404) — Antek, Mar 06 '18 at 09:39

vadian · Accepted Answer · 2017-10-19T09:02:16.963

16

The error is quite clear. JSONDecoder maps NSNull to nil so the decoder throws an error if it's going to decode a nil value to a non-optional type.

The solution is to declare all affected properties as optional.

let title: String
let description : String?
let url : String
let urlToImage : String?

or customize the decoder to replace nil with an empty string.

And because JSONDecoder maps NSNull to nil the check if ... == NSNull.self { is useless.

Edit:

Don't use ugly C-style index based loops use

 let response =  try JSONDecoder().decode(Response.self , from : data)
 for article in response.articles {
      beforeLoadNewsViewController.titleArray.append(article.title)
 }

PS: But why for heaven's sake do you map the article instance to – apparently – separate arrays? You got the Article instances which contain everything related to one article respectively.

edited Oct 19 '17 at 09:02

answered Oct 19 '17 at 07:55

vadian

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so I used this But I will receive Fatal Error – Saeed Rahmatolahi Oct 19 '17 at 08:00
@SaeedRahmatolahi In which line? – vadian Oct 19 '17 at 08:02
beforeLoadNewsViewController.descArray.append(article.articles[i].description!) – Saeed Rahmatolahi Oct 19 '17 at 08:03
Then the decoding works fine. Is `titleArray` in `beforeLoadNewsViewController` initialized? – vadian Oct 19 '17 at 08:06
what are you mean ? Sorry I didn't understand – Saeed Rahmatolahi Oct 19 '17 at 08:08
I don't think its related because the print(article.articles[i].description!) will cause Fatal Error to before that – Saeed Rahmatolahi Oct 19 '17 at 08:11
But the print of print(article.articles[i].description!) before that line will cause Fatal error too – Saeed Rahmatolahi Oct 19 '17 at 08:12
1

I see, `descArray` is not mentioned in the code. But since `description` can be `nil`, don't forced unwrap it. Write `print(article.articles[i].description ?? "n/a")` – vadian Oct 19 '17 at 08:13
the image has problem now can you edit your codes for image too? – Saeed Rahmatolahi Oct 19 '17 at 08:36
What codes? The image does not appear in **your** code. Once again: **Never** forced unwrap optionals which can be `nil` – vadian Oct 19 '17 at 08:43
ok now every things looks good the problem is just images for when the image url is empty I want to use image in my app – Saeed Rahmatolahi Oct 19 '17 at 08:52
Sorry, I cannot read your mind. Please edit your question and add the relevant code and a description. – vadian Oct 19 '17 at 08:53
look now every things are ok I just need to know how to get url of the images that i copied into my application to show them instead of nil images in my application and I edited the code for images to show – Saeed Rahmatolahi Oct 19 '17 at 09:33

score 0 · Answer 2 · answered Oct 17 '17 at 16:42

0

I am sorry, I cannot comment yet. But why don't you test for "null" the way, you did at the URLSession data check, with the guard-statement?

It would then look like:

guard let title = article.articles[i].title else {
    beforeLoadNewsViewController.titleArray.append("")
    return
}
beforeLoadNewsViewController.titleArray.append(title)

You try to parse a JSON structure here, in case the JSON structure would not fit to your needs, you still expect it to have the according attributes.

Could you also provide your JSON structure and how your decoding

try JSONDecoder().decode(Response.self , from : data)

looks like?

answered Oct 17 '17 at 16:42

I don't have any problems with other urls this son is for news api and in Entertainment Weekly api I have problem because the son contains nil values - one more thing I used your codes But the app won't allow me to run because of guard let line – Saeed Rahmatolahi Oct 17 '17 at 16:47
why not simply `beforeLoadNewsViewController.titleArray.append(article.articles[i].title ?? "")` or without the loop using map `beforeLoadNewsViewController.titleArray = article.articles.map{$0.title ?? ""} ` and if you don't want the empty strings in your array use `article.articles.flatMap{$0.title}` instead – Leo Dabus Oct 17 '17 at 16:47
I used beforeLoadNewsViewController.titleArray.append(article.artic‌les[i].title ?? "") but no difference still there is problem – Saeed Rahmatolahi Oct 18 '17 at 10:36

Unexpected nil in JSON strings

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2 Answers2

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