键盘错误：django BaseModelFormSet清除键错误

Question

我已经构建了转换表单集，并且我想进行验证，因此在表单集中没有双重项目预设可以使用clean。但是当表单集中存在一个空表单时，它将产生错误。这是modelformset_factory错误消息：

KeyError at /saleformformset_update/1024'item 

我的代码：

class SaleTransictionFormSet(BaseModelFormSet):
    def clean(self):
        super().clean()
        """Checks that no two articles have the same title."""
        if any(self.errors):
            # Don't bother validating the formset unless each form is valid on its own
            return
        titles = []

        for form in self.forms :
            title = form.cleaned_data['item']
            if not title == '':
                if title in titles:
                    raise forms.ValidationError(" %s in a set must have distinct titles." % title)
                titles.append(title)

如果它们为空或被标记为删除，我想干净地忽略表单集中的表单。