InlinePanel进入makemigrations ttributeError：'str'对象没有属性'bind_to_model'

Question

我的代码段是：

class HomePageContentItemSmall(HomePageContentItem):
    page = ParentalKey('home.HomePage', \
           related_name='content_items_small')

class HomePageContentItemLarge(HomePageContentItem):
    page = ParentalKey('home.HomePage', \
           related_name='content_items_large')


class HomePage(Page):
    title_text = RichTextField(null=True, blank=True)

    content_panels =  [
        FieldPanel('title', classname="full title"),
        InlinePanel('content_items_small', label="Karte schmal"),
        #InlinePanel('content_items_large', label="Karte breit"),
    ]

当我使用runserver makemigration时，出现AttributeError：'str'对象没有属性'bind_to_model'