Convert all the NOT NULL Columns in a Mysql database to Default NULL

NotNullToDefault.sql

SELECT CONCAT_WS('.',TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME) col,CONCAT('alter table ',TABLE_NAME,' MODIFY COLUMN ', COLUMN_NAME,' ',DATA_TYPE,'(',CHARACTER_MAXIMUM_LENGTH,') NULL DEFAULT NULL') as script_col
  FROM information_schema.COLUMNS
 WHERE is_nullable=0 
 and length(COLUMN_DEFAULT) is NULL and
 CHARACTER_MAXIMUM_LENGTH is not NULL and 
 table_schema = 'dbName' 
 Union
 SELECT CONCAT_WS('.',TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME) col,CONCAT('alter table ',TABLE_NAME,' MODIFY COLUMN ', COLUMN_NAME,' ',DATA_TYPE,' NULL DEFAULT NULL') as script_col
  FROM information_schema.COLUMNS
 WHERE is_nullable=0 
 and length(COLUMN_DEFAULT) is NULL and
 CHARACTER_MAXIMUM_LENGTH is NULL and 
 table_schema = 'dbName'