title: failed to run any pipenv command on windows
body: <p>I'm currently a newbie for creating a virtual environment for my project. I have and only have python 3.8 installed on my computer, I also checked my environment variable all working well. So I just installed pipenv through pip by doing <code>pip install pipenv</code> and I've tried to call it on my command prompt by <code>pipenv</code> which is fine at this point. but I can't seem to call <code>pipenv shell</code> or anything else because it threw me some errors like this</p>
  
  <pre><code>  File "c:\python\lib\site-packages\pipenv\vendor\pythonfinder\pythonfinder.py", line 328, in find_all_python_versions
  path_list = sorted(versions, key=version_sort, reverse=True) AttributeError: 'NoneType' object has no attribute 'version_sort'
  </code></pre>
  
  <p>running other pip commands (e.g virtualenv) runs perfectly fine for me. my pip version is also the lastest and already satisfied.</p>
  
  <p>my current directory for python is under :</p>
  
  <blockquote>
    <p>C:\Python</p>
  </blockquote>
  
  <p>I already look through another source for this particular problem like <a href="https://github.com/pypa/pipenv/issues/4296" rel="nofollow noreferrer">this</a>. and I can't seems to work it out because they mostly use a Unix based solution. I need this for my windows 10. I'm looking forward for your answer. thank you very much</p>