Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/musiclibrarian/sort.py", line 91, in sorter
    return doublesort(model, a, b)
  File "/usr/lib/python2.5/site-packages/musiclibrarian/sort.py", line 74, in sorter
    val=apply(f, (model, a, b)+rest)
  File "/usr/lib/python2.5/site-packages/musiclibrarian/sort.py", line 36, in <lambda>
    return lambda model, a, b, *rest:caseicmp(f(model, a), f(model, b))
  File "/usr/lib/python2.5/site-packages/musiclibrarian/sort.py", line 86, in <lambda>
    doublesort=make_lexicographic_sorter(sort_by(lambda model, iter:safeint(tag('tracknumber')(model, iter))), sort_by(column(treemodel.COLUMN_LABEL)))
  File "/usr/lib/python2.5/site-packages/musiclibrarian/sort.py", line 67, in safeint
    return int(val)
ValueError: invalid literal for int() with base 10: ''