SQL & PL/SQL

Hello,

I have a Customer Table with 10 Rows of Data and when I ran this Update Case When Statement it updated the 5 Rows as I wanted but set the other 5 to NULL

Why?

UPDATE Customer_3

   SET NOTES =

       CASE Customer_ID

            WHEN 191 THEN 'Dads Business Checking'

            WHEN 10  THEN 'Danyelle''s Business Checking for Hair Salon'

            When 189 THEN 'My Checking Account'

            When 11  THEN 'Jordy''s Savings Account'

            When 12  THEN 'Mothers'' Business Checking'

       END;

Thanks.