If you have NULL values in your column, you won't be able to perform functions on it. The way to get around this is by converting the NULL values to 0, which is what the coalesce() function does.
In the Data Pipeline, click the +Add Step button and choose Add Column from the dropdown menu. To replace any column name that could contain NULL values with 0, use the following formula:
coalesce("Column Name", 0)
You'll likely want to hide your original column by adding a Hide Columns step after the Add Column step in the Data Pipeline.