It gets an implicit enclosing Staff when nexted in staff-grouping
contexts, so create an implicit Staff around NullVoice at Score level
aligner = \relative { b'8( c d c) d( d d d) }
words = \lyricmode { la __ la __ }
-\new ChoirStaff <<
+\new ChoirStaff \with {\accepts NullVoice } <<
\new Staff \soprano
\new NullVoice = "aligner" \aligner
\new Lyrics \lyricsto "aligner" \words
\accepts "Lyrics"
\accepts "MensuralStaff"
\accepts "NoteNames"
- \accepts "NullVoice"
\accepts "PetrucciStaff"
\accepts "PianoStaff"
\accepts "RhythmicStaff"