Visual Studio 2017 IWizard ProjectFinishedGenerating project is null

I have the following code in my class that extends IWizard:

public void ProjectFinishedGenerating(Project project)
{
   MessageBox.Show(project.Name);
}

But it gives me the error:

System.NullReferenceException HResult=0x80004003 Message=Object reference not set to an instance of an object.
Saying that project is null. Which is right according to my debugger. However, what on earth causes this? I would've thought the method only gets called with a non-null project. How can I fix this?