ValueError: year 0 is out of range

[bnewbold]

  File "/home/bnewbold/scratch/ingests/scielo/.venv/lib/python3.7/site-packages/xylose/scielodocument.py", line 917, in first_year
    return str(datetime.datetime.strptime(year, '%Y').year)
  File "/usr/lib/python3.7/_strptime.py", line 577, in _strptime_datetime
    tt, fraction, gmtoff_fraction = _strptime(data_string, format)
  File "/usr/lib/python3.7/_strptime.py", line 544, in _strptime
    datetime_date(year, 1, 1).toordinal() + 1
ValueError: year 0 is out of range

Python version: Python 3.7
xylose version: 1.35.4

I think that around here: https://github.com/scieloorg/xylose/blob/master/xylose/scielodocument.py#L954

There should be a check if year == 0 and return None if so.