如何过滤大于或为空?

If I want to filter "greater than or equal to", I can use gte:

MyModel.objects.filter(mydatetimefield__gte=mydate)

Likewise, if I want to filter "is none/null", I can use isnull:

MyModel.objects.filter(mydatetimefield__isnull=mydate)

How can I combine these to filter for "greater than or equal to or is null", so the above filter would return both objects if i) mydatetimefield >= mydate, and ii) mydatetimefield == null?