Not null field with default value

[Tom Byars]

If you add a new record to a table and don't supply a value for a not null field that has a default value, why does MySQL raise an exception stating the field cannot be null? Isn't the idea of a default value that you don't have to supply a value? Is the only way to suppress this exception to make the field a not 'not null' field in which case extra storage is set aside for a possible null value despite the fact a null value will never be assigned?