graphite-project/graphite-web — pull request #495 by aaronfc (2013-11-14 11:38:21+00:00)
Title: Fixing holtWintersAberration error bands have None values.

It is known that holtWintersAberration is giving errors when upper and lower bands have None values.
If there is not any band information 0 aberration should be considered.