My coworker and I are debugging an issue in a WCF service he's working on where a string's length isn't being evaluated correctly. He is running this method to unit test a method in his WCF service:

// Unit test method
public void RemoveAppGroupTest()
{
    string addGroup = "TestGroup";
    string status = string.Empty;
    string message = string.Empty;

    appActiveDirectoryServicesClient.RemoveAppGroup("AOD", addGroup, ref status, ref message);
}


// Inside the WCF service
[OperationBehavior(Impersonation = ImpersonationOption.Required)]
public void RemoveAppGroup(string AppName, string GroupName, ref string Status, ref string Message)
{
    string accessOnDemandDomain = "MyDomain";

    RemoveAppGroupFromDomain(AppName, accessOnDemandDomain, GroupName, ref Status, ref Message);
}

public AppActiveDirectoryDomain(string AppName, string DomainName)
{
    if (string.IsNullOrEmpty(AppName))
    {
        throw new ArgumentNullException("AppName", "You must specify an application name");
    }
}

We tried to step into the .NET source code to see what value string.IsNullOrEmpty was receiving, but the IDE printed this message when we attempted to evaluate the variable: 'Cannot obtain value of local or argument 'value' as it is not available at this instruction pointer, possibly because it has been optimized away.' (None of the projects involved have optimizations enabled). So, we decided to try explicitly setting the value of the variable inside the method itself, immediately before the length check -- but that didn't help.

// Lets try this again.
public AppActiveDirectoryDomain(string AppName, string DomainName)
{
    // Explicitly set the value for testing purposes.
    AppName = "AOD";

    if (AppName == null)
    {
        throw new ArgumentNullException("AppName", "You must specify an application name");
    }

    if (AppName.Length == 0)
    {
        // This exception gets thrown, even though it obviously isn't a zero length string.
        throw new ArgumentNullException("AppName", "You must specify an application name");
    }
}

We're really pulling our hair out on this one. Has anyone else experienced behavior like this? Any tips on debugging it?