python之django python blank=True 仍然需要

在下面的代码中，以某种方式具有 blank=True 的字段仍然是必需的并且不能为 Null

例子:

# Skill train timer 
    class SkillTrainingTimer(models.Model): 
    """ 
    Character Training timer,  keep track fo what skill is in training, and when it is done 
    """ 
    character = models.ForeignKey(Character, unique=True) 
    skill = models.ForeignKey(Skill, blank=True) 
    trainingground = models.ForeignKey(TrainingGround, verbose_name='Training ground') 
    timer = models.DateTimeField() 

现在我这样做了:

train_skill = SkillTrainingTimer( 
        character=some_character_obj, 
        trainingground=some_trainingground_obj, 
        timer = fatetime.datetime.now() 
) 
train_skill.save() 

它开始提示技能不能为Null。我在很多模型和函数中都有这个，到目前为止我只是在其中转储了一些无用的数据。