[Django]-Django Model Field Default to Null

If you specify null=True on the model field then the value will be stored as NULL in the database if the user does not provide a value.

• blank=True
  allows you to input nothing (i.e "", None) and keep it empty.
• null=True
  means the database row is allowed to be NULL.
• default=None
  sets the field to None if no other value is given.