What exception type to throw if a list/collection is empty or null and cannot be iterated (not a parameter)?

Question

Suppose a simple example where a method retrieves a collection (such as a list containing some configuration strings) and tries to examine it in some way:

void Init() {     XmlDocument config = new XmlDocument();     config.Load(someXml);     var list = config.SelectNodes("/root/strings/key"); // Normally, list should not be null or empty      if (list == null || list.Count == 0)         throw new SomeExceptionType(message);   // What kind of exception to throw?      // Iterate list and process/examine its elements     foreach (var e in list) ... } 

In this specific instance, the method cannot continue normally if nothing was retrieved. I'm unsure what exception type to throw in such situations. My options are, as far as I know:

• throw nothing manually and let NullReferenceException be thrown automatically (which doesn't handle empty list situation),

• throw custom exception type (probably not a good idea, as I don't anticipate the caller will try to do anything about the exception, i.e. he won't be looking for a speecific exception type to handle),

• do something else?

Answer 1

Enumerable.First throws System.InvalidOperationException if the collection is empty. So could you, I guess.

throw new InvalidOperationException("Sequence contains no elements"); 

https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.first?view=netframework-4.8

Answer 2

You can create your own exception type for appropriate logic:

public class InitializationException : Exception { } 

and then:

throw new InitializationException {Message = "Collection is empty"};