Vaadin Pie chart takes a strange form when none of the legend labels is selected

Question

I am using Vaadin framework with Spring boot and I need to display a PIE Chart with its contents. The thing is everything is working fine and when I click the legends labels the animation works fine.

Pre-click:

When I click the labels:

Note that when I clicked the labels the pie changed, which is what I want.

But when I click all the labels:

The pie chart turns into this blue I don't even know what this is.

I was wondering if anyone knows how would I access the labels in the legends to check if they are selected via Java and if none of them is selected I wouldn't let the user deselect the last one.

Thank you for your help

Find the chart code here:

 private Component getCompaniesChart() {
        Chart chart = new Chart(ChartType.PIE);
        Configuration conf = chart.getConfiguration();
        DataSeries dataSeries = new DataSeries();
        service.findAllDepartments()
                .forEach(Department -> dataSeries.add(new DataSeriesItem(Department.getName(), Department.getEmployeeCount())));

        Options3d options3d = new Options3d();
        options3d.setEnabled(true);
        options3d.setAlpha(70);
        options3d.setBeta(0);
        conf.getChart().setOptions3d(options3d);

        PlotOptionsPie plotOptions = new PlotOptionsPie();
        plotOptions.setDepth(100);
        plotOptions.setAllowPointSelect(true);
        plotOptions.setShowInLegend(true);
        plotOptions.setShadow(true);
        plotOptions.setSize("200%");

        conf.getLegend().setLabelFormat("{name} ({y})");
        conf.getLegend().setItemMarginTop(100);


        conf.setPlotOptions(plotOptions);
        conf.setSeries(dataSeries);
        conf.getChart().setStyledMode(true);

        return chart;
    }