Model Fields Blank and Empty

blank=True, null=True

pattern	(DB) null	(Form) blank	meaning
①	False	False	This field is required when submitting from a form, and the value stored in the database must not be empty
②	True	True	This field is not required when submitting from a form, it doesn't have to be in the value stored in the database.
③	False	True	This field is not required when submitting from a form, but the value stored in the database must not be empty.
④	True	False	This field must be entered when filling out the form, but the database value can be empty.

Conclusion:

① and ② is ordinary usage
③ is for str field.
- string values such as CharField and TextField, empty values are stored as empty strings instead of null.
- For this reason, only blank = True can be specified for fields that handle character strings.
- It means We want to store "" to DB.
④ is weird.
- since There is a something values definitely from Form, DB never be going to be null.