juju/errors — pull request #4 by howbazaar (2014-07-21 21:54:14+00:00)
Title: Make sure the Trace/Annotate/Wrap functions return nil if the error is nil

There have been a number of times where we want to annotate or trace the error of a function if and only if the error is not nil. Instead of checking at all locations where we want to do this, it makes sense that the functions in the errors package do this for us.