如何使用django rest Framework序列化程序将nullable字段设置为None

我有一个简单的视图,我想用它设置一个可为null的 TimeField 至无:

class Device(models.Model):
    alarm_push = models.TimeField(null=True, blank=True)

class DeviceSettingsSerializer(serializers.ModelSerializer):
    class Meta:
        model = Device
        fields = ('alarm_push',)


class DeviceSettingsView(RetrieveUpdateAPIView):
    serializer_class = DeviceSettingsSerializer
    lookup_field = 'uuid'

    def get_queryset(self):
        return Device.objects.all()

但如果我尝试修补数据,如 {'alarm_push': None} 我得到一个错误,比如 {"alarm_push":["Time has wrong format. Use one of these formats instead: hh:mm[:ss[.uuuuuu]]."]}

如何设置 alarm_push 没有?