tmuxp window_command: ls with two panes

gistfile1.txt

Traceback (most recent call last):
  File "/usr/local/bin/tmuxp", line 9, in <module>
    load_entry_point('tmuxp==0.11.0', 'console_scripts', 'tmuxp')()
  File "/Users/dennis/Documents/code/tmuxp/tmuxp/cli.py", line 977, in main
    command_load(args)
  File "/Users/dennis/Documents/code/tmuxp/tmuxp/cli.py", line 412, in command_load
    command_load(new_args)
  File "/Users/dennis/Documents/code/tmuxp/tmuxp/cli.py", line 428, in command_load
    load_workspace(file_cwd, args)
  File "/Users/dennis/Documents/code/tmuxp/tmuxp/cli.py", line 268, in load_workspace
    builder.build()
  File "/Users/dennis/Documents/code/tmuxp/tmuxp/workspacebuilder.py", line 150, in build
    for w, wconf in self.iter_create_windows(session):
  File "/Users/dennis/Documents/code/tmuxp/tmuxp/workspacebuilder.py", line 224, in iter_create_windows
    w.select_window()
  File "/Users/dennis/Documents/code/tmuxp/tmuxp/window.py", line 298, in select_window
    target = '%s:%s' % (self.get('session_id'), self.get('window_index')),
  File "/usr/local/Cellar/python/2.7.10_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/_abcoll.py", line 382, in get
    return self[key]
  File "/Users/dennis/Documents/code/tmuxp/tmuxp/util.py", line 135, in __getitem__
    return self._TMUX[key]
  File "/Users/dennis/Documents/code/tmuxp/tmuxp/window.py", line 65, in _TMUX
    return list(filter(by, self.server._windows))[0]
IndexError: list index out of range