AmbitusAccidental avoid-slur not set?

[Jay Anderson]

========
\version "2.14.1"

\score {
  \new Score {
    \new Voice \with {\consists Ambitus_engraver} {
      cis4( ees)
    }
  }
}
========

This results in this warning:
warning: Ignoring grob for slur: AmbitusAccidental. avoid-slur not set?

This may be more of a feature request. I believe this warning is
meaningless and should be removed. Since I don't think avoiding the
slur matters for AmbitusAccidental would it be fine to set it to any
value? If so then adding "(avoid-slur . inside)" to the
AmbitusAccidental section of define-grobs.scm would avoid this error.
Is there a better approach? Thanks for the help.

-----Jay