I have the following sample code in VS 2022, C# .NET 6.0:

using System.Xml;

XmlDocument doc = new XmlDocument();
doc.LoadXml("<root/>");
foreach (XmlNode node in doc.SelectNodes("aaa"))
    Console.WriteLine(node.OuterXml);

and am getting "CS8602: Dereference of a possibly null reference" at the doc.SelectNodes line. The code works in the sense that it does not fail but simply does nothing when it does not find a node named 'aaa'. If I put 'root', it finds it. So, as far as I see, I am doing nothing wrong and offending to the compiler.

Yet, the warning is there and seems wrong and therefore annoying. My two questions are:

1. Is it a bug in the compiler warning logic?
2. Is there a better (meaning, short, not superfluous) way to write similar code that searches for all nodes matching a certain XML query and to process them that does not generate the warning?

I found out that I can just add "#pragma warning disable CS8602", but that does not feel like a great solution. Ideally, I would like to take advantage of this warning in other cases that seem to me legitimate unlike this one.

CodePudding user response：

What is the most elegant way to stop getting the error?
In your project file delete <Nullable>enable</Nullable>

Is it a bug in the compiler warning logic?
No

Is there a better (meaning, short, not superfluous) way to write similar code?
"Better" is subjective. I think your code is fine, but this is what the warning wants you to do:

 XmlDocument doc = new XmlDocument();
 doc.LoadXml("<root/>");
 var nodes = doc?.SelectNodes("aaa");
 if (nodes == null)
 {
     //handle this case here
     return;
 }
 foreach (XmlNode node in nodes)
     Console.WriteLine(node.OuterXml);

Or you could do something like this:

XmlDocument doc = new XmlDocument();
doc.LoadXml("<root/>");
foreach (var node in Enumerate(doc?.SelectNodes("aaa")))
    Console.WriteLine(node.OuterXml);

private static IEnumerable<XmlNode> Enumerate(XmlNodeList? list)
{
    if (list == null) yield break;
    foreach (XmlNode item in list)
    {
        yield return item;
    }
}

CodePudding user response：

I now understand that as GSerg commented, the API method being declared as XmlNodeList?(string) is the source of the warning (yet, it never returns null; it returns a non-null reference to an empty list).

My subjective "most elegant" solution that I found so far is to do this:

#pragma warning disable CS8602
foreach (XmlElement item in doc.SelectNodes("..."))
#pragma warning restore CS8602

because that suppresses just this instance, and I can benefit from other instances of this warning that, I dare say, are more legitimate.