App getting crash in consuming API using swift?

I am new in Swift Programming, I have consumed API for my project when the data is available it working perfect, if the data is not available app getting crashes in JSONSerialization, the problem is in data?.count != 0, because data.count getting mostly 2 or some other number. If I try to change that line causing error. I don't know how to solve this, can anyone suggest a solution?

func getData() {
    
    guard let URL = Foundation.URL(string:"http://xxxxx/xxx?xx=\(userid)") else {
        return
    }
    
    let request = URLRequest(url: URL)
    
    let task = URLSession.shared.dataTask(with: request, completionHandler: { data,response,error in
        
        guard error == nil && data != nil else {
            let alert = UIAlertController(title: "Check your Internet Connection", message: "", preferredStyle: .alert)
            self.present(alert, animated: true, completion: nil)
            
            let when = DispatchTime.now() + 3
            
            DispatchQueue.main.asyncAfter(deadline: when) {
                // your code with delay
                alert.dismiss(animated: true, completion: nil)
            }
            
            return
        }
        
        print(data?.count)
        
        if data?.count != 0 {
            let received = try! JSONSerialization.jsonObject(with: data!, options:.allowFragments) //Here getting thread error
            print(received)
        })
        
        task.resume()
    }
}

Solution

The problem is in this part.

if data?.count != 0
{
  let received = try! JSONSerialization.jsonObject(with: data!, options:.allowFragments) //Here getting thread error
        print(received)
}

So rewrite it using if let or guard.

guard let responseData = data else{
   return 
}

Now you can use responseData in JSONSerialization method. So the entire code snippet will look like

 guard let responseData = data else{
       return 
    }

 let received = try! JSONSerialization.jsonObject(with: responseData, options:.allowFragments)
     print(received)

In Swift if let and guard are used for unwrapping optionals. Using the "!" to unwrap an optional will cause a crash if the unwrapped value is nil. We use if let or guard to unwrap optionals safely. So as a thumb rule, you should only use "!" to unwrap optionals when you are 101% sure that it won't contain nil values.