Bongo / mpv stack trace

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  make-process(:name "bongo-mpv" :buffer nil :command ("mpv" nil "/var/folders/l8/vzz9lqbs17s745cykjsg7wr80000gn/T/bongo-mpv.socket" "--no-audio-display" "/Volumes/MEdia/newb/Animals as Leaders/Animals as Leaders/07 The Price of Everything and the Value of Nothing.flac"))
  apply(make-process (:name "bongo-mpv" :buffer nil :command ("mpv" nil "/var/folders/l8/vzz9lqbs17s745cykjsg7wr80000gn/T/bongo-mpv.socket" "--no-audio-display" "/Volumes/MEdia/newb/Animals as Leaders/Animals as Leaders/07 The Price of Everything and the Value of Nothing.flac")))
  start-process("bongo-mpv" nil "mpv" nil "/var/folders/l8/vzz9lqbs17s745cykjsg7wr80000gn/T/bongo-mpv.socket" "--no-audio-display" "/Volumes/MEdia/newb/Animals as Leaders/Animals as Leaders/07 The Price of Everything and the Value of Nothing.flac")
  apply(start-process "bongo-mpv" nil "mpv" (nil "/var/folders/l8/vzz9lqbs17s745cykjsg7wr80000gn/T/bongo-mpv.socket" "--no-audio-display" "/Volumes/MEdia/newb/Animals as Leaders/Animals as Leaders/07 The Price of Everything and the Value of Nothing.flac"))
  bongo-start-mpv-player("/Volumes/MEdia/newb/Animals as Leaders/Animals as Leaders/07 The Price of Everything and the Value of Nothing.flac" nil)
  bongo-play-file("/Volumes/MEdia/newb/Animals as Leaders/Animals as Leaders/07 The Price of Everything and the Value of Nothing.flac" nil)
  bongo-play-line(1007)
  bongo-play-lines(nil)
  bongo-dwim()
  bongo-mouse-dwim((mouse-2 (#<window 8 on *Bongo Library*> 817 (135 . 173) 231234011 nil 817 (14 . 10) nil (7 . 13) (8 . 16))))
  funcall-interactively(bongo-mouse-dwim (mouse-2 (#<window 8 on *Bongo Library*> 817 (135 . 173) 231234011 nil 817 (14 . 10) nil (7 . 13) (8 . 16))))
  call-interactively(bongo-mouse-dwim nil nil)
  command-execute(bongo-mouse-dwim)