graphite-project/graphite-web — pull request #91 by dakotacody (2012-10-31 18:35:09+00:00)
Title: Update safeDiff and safeSum

Graphite usually treats 'None' values as missing data which results in breaks in the lines of the graph. However, the sum and diff functions will basically treat them as a 0 value which can make the graph inaccurate when adding or diffing 2 series. This update checks to make sure that there are at least 2 values to be summed or diffed and if not will not do the diff/sum. This falls more in line with the way that graphite handles 'None' values IMHO.