using default as none in django mdoels
>>> type('')
<class 'str'>
>>> type(None)
<class 'NoneType'>
>>>
Avoid using null on string-based fields such as CharField and TextField.
If a string-based field has null=True, that means it has two possible values for “no data”: NULL, and the empty string.
In most cases, it’s redundant to have two possible values for “no data;”
the Django convention is to use the empty string, not NULL.
One exception is when a CharField has both unique=True and blank=True set.
In this situation, null=True is required to avoid unique constraint violations when saving multiple objects with blank values.