Cannot load file due to double TypeError

Created originally on Bitbucket by Robert Howlett

When attempting to load the attached file with attached script I get a TypeError.

Python Version 3.6.0

Openpyxl version 2.5.0a3

Traceback (most recent call last):
  File "C:\Python36\lib\site-packages\openpyxl\descriptors\base.py", line 57, in _convert
    value = expected_type(value)
TypeError: int() argument must be a string, a bytes-like object or a number, not 'NoneType'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:/Projects/gift_for_openpyxl/report_combine.py", line 14, in <module>
    do_thing("input4.xlsx")
  File "C:/Projects/gift_for_openpyxl/report_combine.py", line 8, in do_thing
    wb = openpyxl.load_workbook(xls)  # TypeError: expected <class 'int'>
  File "C:\Python36\lib\site-packages\openpyxl\reader\excel.py", line 274, in load_workbook
    for c in find_charts(archive, rel.target):
  File "C:\Python36\lib\site-packages\openpyxl\chart\reader.py", line 52, in find_charts
    cs = get_rel(archive, deps, rel.id, ChartSpace)
  File "C:\Python36\lib\site-packages\openpyxl\packaging\relationship.py", line 158, in get_rel
    obj = cls.from_tree(tree)
  File "C:\Python36\lib\site-packages\openpyxl\descriptors\serialisable.py", line 83, in from_tree
    obj = desc.expected_type.from_tree(el)
  File "C:\Python36\lib\site-packages\openpyxl\descriptors\serialisable.py", line 99, in from_tree
    return cls(**attrib)
  File "C:\Python36\lib\site-packages\openpyxl\chart\chartspace.py", line 191, in __init__
    self.fmtId = fmtId
  File "C:\Python36\lib\site-packages\openpyxl\descriptors\nested.py", line 36, in __set__
    super(Nested, self).__set__(instance, value)
  File "C:\Python36\lib\site-packages\openpyxl\descriptors\base.py", line 69, in __set__
    value = _convert(self.expected_type, value)
  File "C:\Python36\lib\site-packages\openpyxl\descriptors\base.py", line 59, in _convert
    raise TypeError('expected ' + str(expected_type))
TypeError: expected <class 'int'>

Attachments: input4.xlsxreport_combine.py