I have a workflow that uses the running total tool to create a running total of sales in the year, the running total tool shows the average sales for each year. The issue is if a store has 0 sales for the month of January it's because that store was closed, so I don't want that month to be included in my running total and bring my average down. Is there a way to exclude null month/sales values so that they aren't included in my running total tool?