Django (fields.W340) null has no effect on ManyToManyField.

class Customer(models.Model):
    name = models.CharField(verbose_name='客户名', max_length=128)
    contact = models.CharField(verbose_name='电话', max_length=11)
    address = models.CharField(verbose_name='地址', max_length=128)

    status_choices = (
        (0, '意向客户'),
        (3, '已报价'),
        (1, '已拿样'),
        (2, '已成交')
    )

    status = models.IntegerField(choices=status_choices, verbose_name='状态')

    company = models.CharField(verbose_name='公司名', max_length=128, null=True, blank=True)

    create_time = models.DateField(verbose_name='创建时间', auto_now=True)

    product = models.ManyToManyField(Product, verbose_name='意向产品',null=True, blank=True)

    description = models.TextField(verbose_name='备注', null=True, blank=True)

(fields.W340) null has no effect on ManyToManyField.

product = models.ManyToManyField(Product, verbose_name='意向产品', blank=True)