c# System.ArgumentNullException: Value cannot be null. Parameter name: source

Question

The program that I have created needs to read information from a website and then store it. I am getting the error:

System.ArgumentNullException: Value cannot be null.
Parameter name: source
at System.Linq.Enumerable.Select[TSource,TResult](IEnumerable1 source, Func2 selector)

However it does not always run in error. As in sometimes it works and sometimes it doesn't work. How can this be? Here is the code that is giving me the error line 4.

IEnumerable<string> webtemp = Enumerable.Empty<string>();
if (datastring.Contains("today_nowcard-temp"))
{
    webtemp = doc.DocumentNode.SelectNodes("//div[@class = 'today_nowcard-temp']/span").Select(d => d.InnerText.Trim());

    foreach (var this_header in webtemp)
    {
        string[] temporary = this_header.Trim().Replace("Â", "-").Replace(" ", "-").Split('-');
        int f = (Convert.ToInt32(temporary[0]));
        _actualData[0].temp = GetCelsius(f);
        //Console.WriteLine(_actualData[0].temp);
    }
}

this DocumentNode.SelectNodes("//div[@class = 'today_nowcard-temp']/span") returns an null but without seeing what you have in doc it is impossible to say why that xpath doesn't return an result. — rene
– rene, Commented Aug 3, 2017 at 16:17
It returns a result sometimes and from what I can tell the xpath doesn't change. — T.W.
– T.W., Commented Aug 3, 2017 at 16:18
We need to see the xml of your document is was @rene is getting at. — interesting-name-here
– interesting-name-here, Commented Aug 3, 2017 at 16:19
Looks like you're having a similar issues as this: stackoverflow.com/questions/38166949/… — rene
– rene, Commented Aug 3, 2017 at 16:19
@T.W.: Chances are that even though your xpath is not changing that the document you are downloading is. — Chris
– Chris, Commented Aug 3, 2017 at 16:24

Manish Kumar · Accepted Answer · 2017-08-03 16:21:50Z

3

Reason behind this exception is the value that is returned by your SelectNodes method. Sometimes it returns null and then you try to perform Linq operation on null and it generate error. So you can perform a null check on this

var temp= doc.DocumentNode.SelectNodes("//div[@class = 'today_nowcard-temp']/span");

if(temp != null){
//TODO
}

answered Aug 3, 2017 at 16:21

Manish Kumar

1,5852 gold badges16 silver badges24 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

c# System.ArgumentNullException: Value cannot be null. Parameter name: source

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related