puppetlabs/puppet — pull request #2179 by hlindberg (2013-12-20 21:43:38+00:00)
Title: (maint) Provide option to 4x->3x convert to handle :undef differently

Functions requires :undef conversion to '', while other parts
require :undef (verbatim). This changes the signature of the convert
method to accept the value to use when :undef is encountered.