Django get_object() takes exactly 3 arguments (4 given)

when you override get_object() method in model admin Django 1.8 version we will get error message, django get_object() takes exactly 3 arguments (4 given)

In Django 1.8 you need to pass attribute  from_field

def get_object(self, request, object_id, from_field=None):
    obj = super(MyModelAdmin, self).get_object(request, object_id)
    if obj is not None:
        obj.myfield = obj.category.split("|")
    return obj