Replacing nulls when adding across columns

user18610

I have a table which contains null values, and I want to get a dynamic (i.e. it responds to filters - therefore has to be done in beast mode, as I understand) total of values across three columns, keeping null values in the orignal columns but treating them as '0's for the purpose of the calculation. I have tried several methods none of which work, my most recent attempt is:

 

(case when LENGTH(`2016`) = 0 then 0 else `2016` end)+
(case when LENGTH(`2017`) = 0 then 0 else `2017` end)+
(case when LENGTH(`2018`) = 0 then 0 else `2018` end)

Can anyone point out where I am going wrong? For context, I want to use the new column ultimately to calculate a % of grand total (of displayed data), and belive this is the first step.

user18610

Solution was 

(CASE WHEN `2016` IS NULL THEN '0' ELSE `2016` END)+
(CASE WHEN `2017` IS NULL THEN '0' ELSE `2017` END)+
(CASE WHEN `2018` IS NULL THEN '0' ELSE `2018` END)

I think NULL has to be capitalised, as I had tried somethign simiilar before without success.