Update some records in the database table

I want to update two records from the age column in the table below, for this I use the following command:

UPDATE `persons` SET `Age` =( CASE WHEN FirstName = 'User 2' THEN 10 WHEN FirstName = 'User 3' THEN 12 END ) WHERE LastName = 'User'; 

According to the picture below, the rest of the age records are equal to null

Please guide me to solve this problem

>Solution :

use this query:

UPDATE `persons` SET `Age` = ( CASE WHEN FirstName = 'User 2' THEN 10 WHEN FirstName = 'User 3' THEN 12 ELSE Age END ) WHERE LastName = 'User';