Schema module reports errors

Schema module reports errors in twitter schema.

twitter_user.screen_name is part of the primary key but is not specified to be 'not null'.

Full output from Mismatch below:
twitter_user
o column screen_name:
declared: array('type' => 'varchar', 'length' => 255)
actual: array('type' => 'varchar', 'length' => '255', 'not null' => TRUE, 'default' => '')
o column screen_name:
declared: array('type' => 'varchar', 'length' => 255)
actual: array('type' => 'varchar', 'length' => '255', 'not null' => TRUE, 'default' => '')
o column password: key 'not null' not set, ignoring inspected default value