Unexpected Exception (list index out of range) in 2.0

After updating Indico to 2.0 (2.0.3) from 0.99, following Unexpected Exception sometimes occurred.

Probably the URL of https://indico2[.]riken[.]jp/event/2450/program.pdf’ existed in indico 0.99, while the access to the URL in indico 2.0 results Unexpected Exception.
This access came from google bot.
Although this is not severe, is there any solution to avoid this exception ?

subject: Unexpected Exception occurred at indico2[.]riken[.]jp: list index out of range

2018-04-03 01:30:15,224  6ffffbc18a584fcd  indico.flask - ERROR errors.py:107 -- list index out of range

Traceback (most recent call last):
  File "/opt/indico/.venv/lib/python2.7/site-packages/flask/app.py", line 1612, in full_dispatch_request
    rv = self.dispatch_request()
  File "/opt/indico/.venv/lib/python2.7/site-packages/flask/app.py", line 1598, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/opt/indico/.venv/lib/python2.7/site-packages/indico/web/flask/util.py", line 114, in wrapper
    return obj().process()
  File "/opt/indico/.venv/lib/python2.7/site-packages/indico/web/rh.py", line 270, in process
    res = self._do_process()
  File "/opt/indico/.venv/lib/python2.7/site-packages/indico/modules/events/controllers/base.py", line 63, in _do_process
    return RHEventBase._do_process(self)
  File "/opt/indico/.venv/lib/python2.7/site-packages/indico/web/rh.py", line 249, in _do_process
    return self._process()
  File "/opt/indico/.venv/lib/python2.7/site-packages/indico/modules/events/tracks/controllers.py", line 141, in _process
    return send_file('program.pdf', BytesIO(pdf.getPDFBin()), 'application/pdf')
  File "/opt/indico/.venv/lib/python2.7/site-packages/indico/legacy/pdfinterface/base.py", line 425, in getPDFBin
    self._doc.build(self._story, onFirstPage=self.firstPage, onLaterPages=self.laterPages)
  File "/opt/indico/.venv/lib/python2.7/site-packages/reportlab/platypus/doctemplate.py", line 1213, in build
    BaseDocTemplate.build(self,flowables, canvasmaker=canvasmaker)
  File "/opt/indico/.venv/lib/python2.7/site-packages/reportlab/platypus/doctemplate.py", line 969, in build
    self.handle_flowable(flowables)
  File "/opt/indico/.venv/lib/python2.7/site-packages/reportlab/platypus/doctemplate.py", line 834, in handle_flowable
    if frame.add(f, canv, trySplit=self.allowSplitting):
  File "/opt/indico/.venv/lib/python2.7/site-packages/reportlab/platypus/frames.py", line 167, in _add
    w, h = flowable.wrap(aW, h)
  File "/opt/indico/.venv/lib/python2.7/site-packages/reportlab/platypus/paragraph.py", line 1199, in wrap
    blPara = self.breakLines(self._wrapWidths)
  File "/opt/indico/.venv/lib/python2.7/site-packages/reportlab/platypus/paragraph.py", line 1450, in breakLines
    _words = _getFragWords(frags,maxWidth)
  File "/opt/indico/.venv/lib/python2.7/site-packages/reportlab/platypus/paragraph.py", line 537, in _getFragWords
    w = S[-1]
IndexError: list index out of range

{u'data': {u'get': {},
           u'headers': {'Accept': u'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
                        'Accept-Encoding': u'gzip,deflate,br',
                        'Connection': u'keep-alive',
                        'From': u'googlebot(at)googlebot.com',
                        'Host': u'indico2[.]riken[.]jp',
                        'User-Agent': u'Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)'},
           u'json': None,
           u'post': {},
           u'url': {'confId': u'2450'}},
 u'endpoint': u'tracks.program_pdf',
 u'id': '6ffffbc18a584fcd',
 u'ip': '66.249.71.132',
 u'method': 'GET',
 u'referrer': None,
 u'rh': 'RHTracksPDF',
 u'time': '2018-04-03T01:30:15.293621',
 u'url': u'https://indico2[.]riken[.]jp/event/2450/program.pdf',
 u'user': None,
 u'user_agent': u'Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)'}