Hi,
Giving a try to the current gaupol from git in a live session of Fedora 24 Workstation:

• Open gaupol and create a new document. Note that the "Preview in external video player" button in the main menu toolbar is disabled, as it's expected.
• Click to edit the text of the unique subtitle created by default. NO add any text to it. Click outside of it to close the edition mode.
• Now the Preview button is found enabled. Clicking in it triggers an error:

File: /home/liveuser/Descargas/gaupol-0.91/gaupol/agents/preview.py
Line: 63
In: _on_preview_activate

    self.preview(page, position, doc)

File: /home/liveuser/Descargas/gaupol-0.91/gaupol/agents/preview.py
Line: 73
In: preview

    position, doc, command, offset, encoding, temp)

File: /home/liveuser/Descargas/gaupol-0.91/aeidon/agents/preview.py
Line: 123
In: preview

    VIDEOFILE=aeidon.util.shell_quote(self.video_path))

File: /home/liveuser/Descargas/gaupol-0.91/aeidon/util.py
Line: 407
In: shell_quote

    path = path.replace("", "\")

AttributeError: 'NoneType' object has no attribute 'replace'

Environment

Platform: Linux-4.5.5-300.fc24.i686-i686-with-fedora-24-Twenty_Four
Locale: es_ES.utf_8

Versions

aeidon: 0.91
chardet: 2.2.1
enchant: 1.6.6
gaupol: 0.91
gstreamer: 1.8.1.0
gtk+: 3.20.6
pygobject: 3.20.1
python: 3.5.1