change_column_null

Sets or removes a +NOT NULL+ constraint on a column. The null flag indicates whether the value can be NULL. For example

says nicknames cannot be NULL (adds the constraint), whereas

allows them to be NULL (drops the constraint).

The method accepts an optional fourth argument to replace existing +NULL+s with some other value. Use that one when enabling the constraint if needed, since otherwise those rows would not be valid.

Please note the fourth argument does not set a column's default.