Django: non-nullable field without a default

Question

In Django I use manage.py makemigrations and manage.py migrate on the following models.py file:

class Family(models.Model):
    comment1 = models.CharField(max_length=80)
    #comment2 = models.CharField(max_length=80)

After this successful initialization, I changed models.py to (I just uncomment the new model field which is basically a copy of the other model field):

class Family(models.Model):
    comment1 = models.CharField(max_length=80)
    comment2 = models.CharField(max_length=80)

Now when I try to makemigrations again I get the following error:

You are trying to add a non-nullable field 'comment' to family without a default; we can't do that (the database needs something to populate existing rows).

Please select a fix:

1) Provide a one-off default now (will be set on all existing rows with a null value for this column)

2) Quit, and let me add a default in models.py Select an option:

Why didn't I get this error upon intialization in the first place?

Answer 1

Others are right. you should set a default value for that field. but there is a a trick that you can solve this. but it is not a good way... only if you have no choice.
1. comment all of your table
2. run makemigrations and migrate
3. uncomment your table
4.2. run makemigrations and migrate again

Answer 2

image1=models.ImageField(upload_to='app/image12',help_text="hi", null=True)

That is, set null= True'in the field.

It happens when you change your model after stored database.