Blended Data Sum

Hi all!

I have an issue that I have been trying to fix for a while. I am trying to obtain the sum of 2 Values (Cost1, Cost2) that are coming from 2 different data sources. I have created the Blended Data and joined it according to Date. The problem is when 1 of the 2 values is null, the calculation doesn't work: instead of displaying the total for the value that is not null, it displays an error. Can anyone help with this? Thank you in advance

0 1 111