[FIX] Charts: Fix tooltip value when data is zero

Following a refactoring of the charts, the tooltip would not display the
data value when the data equalled zero.

How to reproduce:
- generate a line graph such that one of the dataset points is 0
- Hover the said data point

-> the tooltip will read something along "Series 1:" and no value
afterwards.

closes #5128

Task: 4251681
X-original-commit: 9f337f3
Signed-off-by: Pierre Rousseau (pro) <[email protected]>

src/helpers/figures/charts/chart_ui_common.ts

@@ -166,7 +166,7 @@ export function getDefaultChartJsRuntime(
             const xLabel = tooltipItem.dataset?.label || tooltipItem.label;
             // tooltipItem.parsed can be an object or a number for pie charts
             let yLabel = horizontalChart ? tooltipItem.parsed.x : tooltipItem.parsed.y;
-            if (!yLabel) {
+            if (yLabel === undefined || yLabel === null) {
               yLabel = tooltipItem.parsed;
             }
 

tests/figures/chart/chart_plugin.test.ts

@@ -2034,6 +2034,18 @@ describe("Chart design configuration", () => {
       }
     );
 
+    test.each(["bar", "line"])(
+      "Basic chart tooltip label, zero-values are properly displayed",
+      (chartType) => {
+        setCellContent(model, "A2", "0");
+        createChart(model, { ...defaultChart, type: chartType as "bar" | "line" }, "42");
+        const runtime = model.getters.getChartRuntime("42") as BarChartRuntime;
+        const label = getTooltipLabel(runtime, 0, 0);
+
+        expect(label).toEqual("0");
+      }
+    );
+
     test.each(["line", "scatter", "combo", "bar"] as const)(
       "%s chart with no title but a legend have the correct padding",
       (chartType) => {