can't use feed2exec with debian package

Got exception AttributeError: 'NoneType' object has no attribute 'startswith' for many commands

Describe the general problem you have found here.

How to reproduce

1. install unstable package in a stretch system
2. try command feed2exec ls

Expected behavior

Display that there's no configured feeds

Actual behavior

$ feed2exec ls                      
Traceback (most recent call last):
  File "/usr/bin/feed2exec", line 11, in <module>
    load_entry_point('feed2exec==0.10.0', 'console_scripts', 'feed2exec')()
  File "/usr/lib/python3/dist-packages/click/core.py", line 716, in __call__
    return self.main(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/click/core.py", line 696, in main
    rv = self.invoke(ctx)
  File "/usr/lib/python3/dist-packages/click/core.py", line 1060, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/lib/python3/dist-packages/click/core.py", line 889, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/lib/python3/dist-packages/click/core.py", line 534, in invoke
    return callback(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/feed2exec/__main__.py", line 86, in ls
    st = FeedManager()
  File "/usr/lib/python3/dist-packages/feed2exec/feeds.py", line 276, in __init__
    self.path = os.path.expanduser(ConfFeedStorage.path)
  File "/usr/lib/python3.5/posixpath.py", line 229, in expanduser
    if not path.startswith(tilde):
AttributeError: 'NoneType' object has no attribute 'startswith'

Environment

• Version: feed2exec, version 0.10.0
• Operating system: Linux littlegr82 4.9.0-5-amd64 #1 SMP Debian 4.9.65-3+deb9u2 (2018-01-04) x86_64 GNU/Linux
• Install method: apt install feed2exec feed2exec-doc * URL: e.g. https://example.com/feed.rss