Calculations with Empty fields
By design, Abacus does not run a formula if the related fields are empty. But in some cases, a formula may need to be calculated even if the field is empty. There are a couple work arounds to this issues.
Make sure the fields used in the formula have a default value. This can be done by configuring the field and setting a default value. The downside to this is the you Jira issue may have all these useless values always showing on your screen.
The second option is to have Abacus populate a default value for you if it is empty. To implement this solution, you can add a condition to check if the field is empty. Then add action to Edit Issue and set a default number.
Add the formula you intend to calculate right after the Edit issue action otherwise calculate formal as is.