if you query a mysql database and ask for all rows that do not have a specific value in a specific field, you might expect to also get those rows where the field is null.
but this is not the case.
so if you want to get all rows you have to query all rows that do not have the specific value in this field or where this is field is null.
or in code
select * from database where field not like '%value%'
select * from database where field not like '%value%' or field is null