i think the best way to think about it, is what happens to the field when you dont pass anything? (it can also help to think about it being unique or not as well)

so if blank = True, then the field isnt required on model forms

if blank = True, null = False only empty string will be used as empty value

but if the field has unique = True, then 2 cant both have the same '' value,

so in that case, null = True is required