Converter to Bool

I have a normal Checkbox, where I want to set the IsChecked property to a Binding resource. The resource is a self written class myClass, which can be null or referenced (means not null).

The Checkbox should be NOT checked, if the assigned object myObject (out of myClass) is null
and checked, if it is not null.

What do I have to write in the IsChecked="..." property in my xaml file?