# Buggy code
def _refresh_outlineexplorer(self, index=None, update=True, clear=False):
    """Refresh outline explorer panel"""
    oe = self.outlineexplorer
    if oe is None:
        return
    if index is None:
        index = self.get_stack_index()
    if self.data:
        finfo = self.data[index]
        oe.setEnabled(True)
        if finfo.editor.oe_proxy is None:
            finfo.editor.oe_proxy = OutlineExplorerProxyEditor(
                finfo.editor, finfo.filename
            )
        oe.set_current_editor(finfo.editor.oe_proxy, update=update, clear=clear)
        if index != self.get_stack_index():
            # The last file added to the outline explorer is not the
            # currently focused one in the editor stack. Therefore,
            # we need to force a refresh of the outline explorer to set
            # the current editor to the currently focused one in the
            # editor stack. See spyder-ide/spyder#8015.
            self._refresh_outlineexplorer(update=False)
            return
    self._sync_outlineexplorer_file_order()


# Traceback (IndexError)
File "C:\Users\Daniel\Anaconda3\envs\4v\lib\site-packages\spyder\plugins\editor\plugin.py", line 1901, in load
self.switch_to_plugin()
File "C:\Users\Daniel\Anaconda3\envs\4v\lib\site-packages\spyder\plugins\editor\plugin.py", line 1437, in switch_to_plugin
super(Editor, self).switch_to_plugin()
File "C:\Users\Daniel\Anaconda3\envs\4v\lib\site-packages\spyder\api\plugins.py", line 355, in switch_to_plugin
super(BasePluginWidget, self)._switch_to_plugin()
File "C:\Users\Daniel\Anaconda3\envs\4v\lib\site-packages\spyder\plugins\base.py", line 290, in _switch_to_plugin
self._visibility_changed(True)
File "C:\Users\Daniel\Anaconda3\envs\4v\lib\site-packages\spyder\plugins\editor\plugin.py", line 346, in _visibility_changed
SpyderPluginWidget._visibility_changed(self, enable)
File "C:\Users\Daniel\Anaconda3\envs\4v\lib\site-packages\spyder\plugins\base.py", line 388, in _visibility_changed
self.refresh_plugin()
File "C:\Users\Daniel\Anaconda3\envs\4v\lib\site-packages\spyder\plugins\editor\plugin.py", line 360, in refresh_plugin
editorstack.refresh()
File "C:\Users\Daniel\Anaconda3\envs\4v\lib\site-packages\spyder\plugins\editor\widgets\editor.py", line 2404, in refresh
self._refresh_outlineexplorer(index, update=False)
File "C:\Users\Daniel\Anaconda3\envs\4v\lib\site-packages\spyder\plugins\editor\widgets\editor.py", line 2283, in _refresh_outlineexplorer
finfo = self.data[index]
IndexError: list index out of range

# Fixed code
def _refresh_outlineexplorer(self, index=None, update=True, clear=False):
    """Refresh outline explorer panel"""
    oe = self.outlineexplorer
    if oe is None:
        return
    if index is None:
        index = self.get_stack_index()
    if self.data and len(self.data) > index:
        finfo = self.data[index]
        oe.setEnabled(True)
        if finfo.editor.oe_proxy is None:
            finfo.editor.oe_proxy = OutlineExplorerProxyEditor(
                finfo.editor, finfo.filename
            )
        oe.set_current_editor(finfo.editor.oe_proxy, update=update, clear=clear)
        if index != self.get_stack_index():
            # The last file added to the outline explorer is not the
            # currently focused one in the editor stack. Therefore,
            # we need to force a refresh of the outline explorer to set
            # the current editor to the currently focused one in the
            # editor stack. See spyder-ide/spyder#8015.
            self._refresh_outlineexplorer(update=False)
            return
    self._sync_outlineexplorer_file_order()