IndexError: list index out of range (after clicking on "Update Plot")

[florianneukirchen]

Describe the bug
"IndexError: list index out of range" after clicking on "Update Plot".
This only happens when I click on "Update Plot" in the wrong moment, after changing from scatter plot to ternary plot or to violin plot. Stack trace see below

To Reproduce
Steps to reproduce the behavior:

1. Open e.g. countries layer from Natural Earth (or any other layer)
2. Set up a scatter plot (e.g. Xfield POP_EST, Yfield GDP_MD)
3. "Create Plot"
4. Switch to ternary plot
5. eventually add a Zfield
6. Click "update plot"
7. Raises IndexError
8. Now click "Create Plot"
9. Raises the same IndexError

• This also happens when switching to Violin plot in point 4
• This does not happen if I click "create plot" in point 6

Desktop (please complete the following information):

• OS: Linux Mint 21.2
• QGIS release 3.40.3 (official package) and 3.42.1 (from conda-forge)
• DataPlotly release 4.2.0

Additional context
IndexError: list index out of range
Traceback (most recent call last):
File "/home/riannek/.local/share/QGIS/QGIS3/profiles/default/python/plugins/DataPlotly/gui/plot_settings_widget.py", line 1480, in UpdatePlot
self.create_plot()
File "/home/riannek/.local/share/QGIS/QGIS3/profiles/default/python/plugins/DataPlotly/gui/plot_settings_widget.py", line 1417, in create_plot
plot_factory = self.create_plot_factory()
File "/home/riannek/.local/share/QGIS/QGIS3/profiles/default/python/plugins/DataPlotly/gui/plot_settings_widget.py", line 1373, in create_plot_factory
plot_factory = PlotFactory(settings, visible_region=visible_region)
File "/home/riannek/.local/share/QGIS/QGIS3/profiles/default/python/plugins/DataPlotly/core/plot_factory.py", line 117, in init
self.rebuild()
File "/home/riannek/.local/share/QGIS/QGIS3/profiles/default/python/plugins/DataPlotly/core/plot_factory.py", line 445, in rebuild
self.trace = self._build_trace()
File "/home/riannek/.local/share/QGIS/QGIS3/profiles/default/python/plugins/DataPlotly/core/plot_factory.py", line 462, in _build_trace
return PlotFactory.PLOT_TYPES[self.settings.plot_type].create_trace(self.settings)
File "/home/riannek/.local/share/QGIS/QGIS3/profiles/default/python/plugins/DataPlotly/core/plot_types/ternary.py", line 38, in create_trace
text = [
File "/home/riannek/.local/share/QGIS/QGIS3/profiles/default/python/plugins/DataPlotly/core/plot_types/ternary.py", line 43, in
settings.properties['z_name'], settings.z[k]) for k
IndexError: list index out of range