Check the MetaModel Existence while Running a Dynamic Data Application

In the web application that I’m developing using Dynamic Data, I set the DataContext at runtime. The application might bind different contexts depending on many variables. I usually test it on two different browsers, and, because of the session, I need to pass the same procedure twice. The second time, the DataContext is already set, so I don’t need to register the context anymore. The simple condition I use:

if (System.Web.DynamicData.MetaModel.Default == null)
{
    // Register context and routes
    ...
}

Otherwise I would get this exception:

[ArgumentException: L'elemento è già stato aggiunto. 
Chiave nel dizionario: 'MyAppDataContext'. 
Chiave aggiunta: 'MyAppDataContext']

Meaning: The item is already present. Key in dictionary ‘MyAppDataContext’, Key added ‘MyAppDataContext’.