new migrations coming up when blank=True in booleanfield in django 2.1+

[anvesh Agarwal]

As document says, https://docs.djangoproject.com/en/2.2/ref/models/fields/#booleanfield previously blank=True was implicit but in django 2.1+ , we have to add it externally. So i dont understand why new migrations are coming up for this? Does this mean that previously blank=True wasnt considered for the migrations?