Almost every time the average cross-section tool is called, a warning is raised: `RuntimeWarning: Mean of empty slice.`. This is another regression introduced with PlotPy V1 (was not present in [guiqwt](https://github.com/PlotPyStack/guiqwt) V4).
Almost every time the average cross-section tool is called, a warning is raised:
RuntimeWarning: Mean of empty slice..This is another regression introduced with PlotPy V1 (was not present in guiqwt V4).