fix(DashboardChartSummary): use null for nullable values

See: BEDS-1548

Author: enzo-bitfly

frontend/components/dashboard/chart/DashboardChartSummary.vue

@@ -208,7 +208,11 @@ const loadData = async () => {
           name = getGroupLabel($t, element.id, groups.value, allGroups)
         }
 
-        const data = element.data.map(datapoint => datapoint !== undefined ? datapoint * 100 : undefined)
+        const data = element.data.map(datapoint =>
+          (datapoint === null || datapoint === undefined)
+            ? null
+            : datapoint * 100,
+        )
 
         const newObj: SeriesOption = {
           connectNulls: false,