\version "2.19.49"
\language "english"

origBreak = { \break }

ThirdTune =
\relative {
   \repeat volta 2 {
     \time 4/4
     \key g \major
     | e''4 e g8 e d b
     | e8 d b a d4 b
     | e4 e g8 e g4
     | a2 g
     \origBreak
     | e4 e g8 e d b
     | e8 d b a d4 b
     | e4 d8 b d b a g
     | b8 a g4 e2
     \origBreak
   }
   \repeat volta 2 {
     | b'4 a8 g e4 b'
     | a8 g e g a4 b
     | d2 cs2
     | c2 a
     | b4 a8 g e4 b'
     \origBreak
     | a8 g e d g4 e
   }
   \alternative {
     {
       | b4 d8 d b4 d
       | ds4 b ds8 fs a4
     }
     {
       | g8 c c c b4 g
       | a8 fs d4 e2
     }
   }
}

ThirdTuneChords = \chordmode {
   \repeat volta 2 {
     | e1:m s s a2 g
     | e1:m s e2:m d b:7 e:m
     | e1:m s d2 a c b:7 e1:m
     | s1
   }
   \alternative {
     { d1 b1:7 }
     { c2 g d e:m }
   }
}

\score {
   <<
     \new ChordNames \ThirdTuneChords
     \new Staff { \clef treble \ThirdTune }
   >>  
   \layout {
     indent = 0 \in
     \override Score.BarNumber.break-visibility = #'#(#f #f #f)
   }
}

File "/usr/lib/python3/dist-packages/ly/musicxml/lymus2musxml.py", line 
96, in parse_text
self.parse_document(doc)
File "/usr/lib/python3/dist-packages/ly/musicxml/lymus2musxml.py", line 
109, in parse_document
self.parse_tree(mustree)
File "/usr/lib/python3/dist-packages/ly/musicxml/lymus2musxml.py", line 
123, in parse_tree
self.parse_nodes(mus_nodes)
File "/usr/lib/python3/dist-packages/ly/musicxml/lymus2musxml.py", line 
135, in parse_nodes
func_call(m)
File "/usr/lib/python3/dist-packages/ly/musicxml/lymus2musxml.py", line 
173, in Assignment
self.mediator.new_header_assignment(a.name(), val)
UnboundLocalError: local variable 'val' referenced before assignment