D.C. al fine, and "volta spanner" errors

[Graham King]

Following on from an earlier thread[1], I have a snippet, below, that uses a repeat to create a "D.C. al fine" structure.

The snippet throws two warnings: "cannot end volta spanner" that appear to be caused by the "\set Score.repeatCommands" line.

Whilst I could just bludgeon these unwelcome messages with ly:expect-warning, the conscientious bit of me is asking the list whether they can be eliminated without hurting lilypond's feelings...

>     \version "2.19.35"
>     
>     \repeat volta 2 {
>       c''1
>       \bar "|."
>       \mark "Fine"
>     }
>     \alternative {
>       {
>         % Treat the "B" section as a first-time bar, but
>         % suppress the "|1." label:
>         \set Score.repeatCommands = #'((volta #f))
>         c''1
>         \bar "||"
>         \mark "D.C."
>       }
>       { } % There is no "second-time bar".
>     }
>

[1] https://lists.gnu.org/archive/html/lilypond-user/2016-02/msg00014.html