Что следует передать для параметра @object в BeginInvoke?

I have an event delegate that is defined as follows:

public delegate void CallbackDelegate(Data data);
public event CallbackDelegate OnDataComplete;

I raise the event asynchronously:

// Raise the OnDataComplete event
OnDataComplete.BeginInvoke(new Data(), null, null);

Subsequently, the signature of BeginInvoke looks like:

IAsyncResult CallbackDelegate.BeginInvoke(Data data, AsyncCallback callback, object @object)

In most examples I've seen BeginInvoke is called with the @object parameter being null, but I can't find the documentation which explains what is the purpose of that parameter.

So what is the purpose of that parameter? What can we use it for?