Create and SHow Forms c#

I´m trying to create and show forms in VS 2013 with a generic method this is my method:

void showOrUpdateForm<T>(ref Form form) where T : Form 
{
    if (form == null)
    {
        form = Activator.CreateInstance(typeof(T)) as T;
        form.Show();
    }
    else
        form.WindowState = FormWindowState.Normal;

    form.Focus();
}

this code i got it from here. So when i try to call this method like they told like that:

 myForm1 form;
 showOrUpdateForm<myForm1>(ref form);

It give me error:

Error 1 The best overloaded method match for 'GestionEAS.GestionEAS.showOrUpdateForm(ref System.Windows.Forms.Form)' has some invalid arguments

Error 2 Argument 1: cannot convert from 'ref package.Views.form' to 'ref System.Windows.Forms.Form'

How can I fix this?