Why would Assembly.GetExecutingAssembly() return null?

Question

I am using a xml file as an embedded resource to load an XDocument. We are using the following code to get the appropriate file from the Assembly:

XDocument xd = new XDocument();
Assembly assembly = null;

try
{
    assembly = Assembly.GetExecutingAssembly();
}
catch(Exception ex)
{
    //Write exception to server event log
}

try
{
    if(assembly != null)
    {
        using(StreamReader sr = new 
            StreamReader(assembly.GetManifestResourceStream("assemblyPath")))
        {
            using(XmlTextReader xtr = new XmlTextReader(sr))
            {
                xd = XDocument.Load(xtr);
            }
        }
    }
}
catch(Exception ex)
{
    //Write exception to server event log
}

So when the code is deployed, we occasionally will go to the page and nothing will be loaded from the embedded document. When we check the event log, there is no error. If the user just refreshes the page, it'll load fine. This has lead me to think that, for some reason, assembly = Assembly.GetExecutingAssembly(); is ocassionally returning null, and the way the code is written this isn't an error. So, my question is why would Assembly.GetExecutingAssembly(); be returning null? I found a couple articles talking about there being errors sometimes with unmanaged code, but this application is written in C# and deployed via setup project.

The code was originally written without error avoidance code. It was added to keep the users from getting error screens. The exceptions are written to the event log of the server.

Answer 1

That can return null if you are launching your code from an unmanaged application (e.g. the NUnit Test runner): Try the following using the console:

[Test]
public void att()
{
    Assert.NotNull(Assembly.GetExecutingAssembly());
}

Seeing as you've tagged it embedded, I'm guessing you're using some sort of bootloader, or interpreter to run your .Net app? That would probably be unmanaged (i.e. not .Net interpretted) and hence would return null.

See the documentation, section "Remarks: http://msdn.microsoft.com/en-us/library/system.reflection.assembly.getentryassembly.aspx