Alter TEXT column to NOT NULL when there is existing NULL rows Mysql does not support default values for TEXT columns. I have a live database with NULL values

What is the proper way to change all null values to a predefined value and change the column to not null? I would like to do this in a single transaction to prevent new NULL values being inserted between updating all old NULL values and ALTERING the column.
Run this query:
UPDATE tablename SET textname = "" WHERE textname IS NULL
after running that you can change the table structure so it does not allow null values anymore. 

I recommend checking the code to make sure it doesn't check for null instead of empty strings before changing the way the dB behaves