2.25.2 optional fine endings

[Paul Scott]

The following code derived from NR 1.4.1 "Manual repeats" does what I 
want but gives a warning.  I don't understand the code or documentation 
well enough to do it correctly.

\version "2.25.2"

voltaFine = \markup { \text \upright \fontsize #2 "Fine Ending" }
voltaCont = \markup { \text \upright \fontsize #2 "To Cont." }
\fixed c' {
  c1
  \set Score.repeatCommands = #(list(list 'volta voltaFine))
  c4 d c2 \bar "|."
  \set Score.repeatCommands = #(list(list 'volta voltaCont))
  f4 g a b
  \set Score.repeatCommands = #'((volta #f))
}

TIA for help with this,

Paul