graphite-project/graphite-web — pull request #717 by bruce-lyft (2014-05-15 17:47:40+00:00)
Title: bugfix in perSecond():  if the series has null data, diff the existing d...

...ata.

Consider a series that looks like this:
X1,null,X2,null,X3,null,...
In the current implmenentation, perSecond() will return all nulls
for this series. With this bugfix, perSecond will return instead:
(x2-x1)/step,null,(x3-x2)/step,null,...