In AWS QuickSight, I have a line chart that displays cumulative value of a column over time. I’m using calculated fields with `runningSum()`

function to get the cumulative sum, like so:

`runningSum(sum(COALESCE( NULLIF(col_one, '') , 0 )), [col_two ASC], [col_three])`

The cumulative sum that I get first rises, then drops to zero and then rises again. Now, assuming, or rather considering, that the values in col_one will always be positive, the cumulative sum should never drop to zero once it goes up from zero,