How to make string column with null default?

Hi,

I'm trying to use migrations to create a table with a string column
that has a default value of null. Instead of a default of null,
though, it's using the four-character string "NULL".

I found some similar bug reports (e.g., http://dev.rubyonrails.org/ticket/9469
http://dev.rubyonrails.org/ticket/9145 ), but that second one was
closed with "cannot reproduce/works for me", so I must be doing
something wrong???

This is what I'm doing. I tried this with gem rails 1.2.3 and edge
rails 7416, and they both did the same thing.

$ rails project ; cd project
$ cat > config/database.yml
   development:
     adapter: sqlite3
     database: db/project.development
^D
$ mkdir db/migrate ; cat > db/migrate/001_initial_schema.rb
   class InitialSchema < ActiveRecord::Migration
      def self.up
         create_table :items do |t|
            t.column :name, :string
            # I also tried:
            # t.column :name, :string, :null => true, :default => nil
         end
      end
   end
^D
$ cat > app/models/item.rb
   class Item < ActiveRecord::Base
   end
^D
$ rake db:migrate

$ script/console
Loading development environment.

x = Item.create

=> #<Item id: 1, name: "NULL">

x.name.length

=> 4
^D

$ sqlite3 db/project.development

.schema items

CREATE TABLE items ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
"name" varchar(255) DEFAULT NULL);

insert into items values (69, null);
select * from items;

1|NULL
69|

Thanks for you help,
Steven