Updating App.config

Today I faced the problem to update the App.config. There exist several solutions out there but I was not able to find a simple one. Therefore I decided to try out the new Linq to XML feature of .NET 3.5 and wrote the following method which updates the value of a specific key in the App.config file:

public static void UpdateAppConfig(string key, object value)
{
  if (key == null)
      throw new ArgumentNullException("key");

  if (value == null)
      throw new ArgumentNullException("value");

  XDocument doc = XDocument.Load(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
  var result = (from appSetting in doc.Descendants("appSettings").Descendants("add")
                where appSetting.Attribute("key").Value.Equals(key)
                select appSetting).FirstOrDefault();

  if (result != null)
  {
      result.Attribute("value").SetValue(value);
      doc.Save(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
      doc = null;
  }
  else
  {
      Console.WriteLine("The application setting with key '{0}' was not found!", key);
  }
}