Traceback (most recent call last):
  File "/home/zorin/.local/lib/python3.8/site-packages/isisdl/backend/request_helper.py", line 982, in _download_documents
    return course.download_documents(self)
  File "/home/zorin/.local/lib/python3.8/site-packages/isisdl/backend/request_helper.py", line 701, in download_documents
    all_content.append(PreMediaContainer(file["fileurl"], self, MediaType.document, file["filename"], file["filepath"], file["filesize"], file["timemodified"]))
  File "/home/zorin/.local/lib/python3.8/site-packages/isisdl/backend/request_helper.py", line 179, in __init__
    self.url = normalize_url(url)
  File "/home/zorin/.local/lib/python3.8/site-packages/isisdl/utils.py", line 747, in normalize_url
    if url.endswith("?forcedownload=1"):
AttributeError: 'NoneType' object has no attribute 'endswith'