ValueError: empty string for float() after migrating tickets from Bugzilla To Trac

[Barry]

I have run Bugzilla2Trac and after an issue eventually got the Bugzilla tickets migrated. The first issue was

Traceback (most recent call last):
  File "C:\Python24\Scripts\bugzilla2trac.py", line 887, in ?
    main()
  File "C:\Python24\Scripts\bugzilla2trac.py", line 884, in main
    convert(BZ_DB, BZ_HOST, BZ_USER, BZ_PASSWORD, TRAC_ENV, TRAC_CLEAN)
  File "C:\Python24\Scripts\bugzilla2trac.py", line 780, in convert
    trac.addTicketChange (**ticketChange)
  File "C:\Python24\Scripts\bugzilla2trac.py", line 394, in addTicketChange
    (ticket, time.strftime('%s'), author, field,
  File "C:\Python24\Lib\site-packages\trac\db\util.py", line 50, in execute
    return self.cursor.execute(sql_escape_percent(sql), args)
  File "C:\Python24\Lib\site-packages\trac\db\sqlite_backend.py", line 56, in ex
ecute
    args or [])
  File "C:\Python24\Lib\site-packages\trac\db\sqlite_backend.py", line 48, in n_error
    return function(self, *args, **kwargs)
pysqlite2.dbapi2.IntegrityError: columns ticket, time, field are not unique

I got around this by introducing OR IGNORE in the INSERT INTO ticket & INSERT INTO ticket_changes clause. This migrated the changes

However when I go to Trac and click on "View Tickets" and select "All Tickets By Milestone (Including closed)" I get the following error

Traceback (most recent call last):
  File "C:\Python24\Lib\site-packages\trac\web\main.py", line 387, in dispatch_request
    dispatcher.dispatch(req)
  File "C:\Python24\Lib\site-packages\trac\web\main.py", line 237, in dispatch
    resp = chosen_handler.process_request(req)
  File "C:\Python24\Lib\site-packages\trac\ticket\report.py", line 88, in process_request
    resp = self._render_view(req, db, id)
  File "C:\Python24\Lib\site-packages\trac\ticket\report.py", line 346, in _render_view
    value['date'] = format_date(cell)
  File "C:\Python24\lib\site-packages\trac\util\datefmt.py", line 68, in format_date
    return format_datetime(t, format, gmt)
  File "C:\Python24\lib\site-packages\trac\util\datefmt.py", line 58, in format_datetime
    t = time.localtime(float(t))
ValueError: empty string for float()

[Emmanuel Blot]

(reformatting description)