Fix trendline error

- This MR fixes an error
when adding a date item
to the scatterplot that is
out of the date range. It adds
a sanity check to the
transformScatterData method.

Changelog: fixed
EE: true

ee/app/assets/javascripts/analytics/productivity_analytics/utils.js

@@ -97,7 +97,13 @@ export const transformScatterData = (data, startDate, endDate) => {
 
     if (dayDiff > -1) {
       const idx = totalItems - (dayDiff + 1);
-      result[idx].push(data[id]);
+      // When dealing with different time zones (merged_at is in UTC but endDate is in the browser's timezone)
+      // the computed idx might be out of bounds because the result array (and its length) is initialized
+      // via initDateArray (which takes only the browser's timezone into account)
+      // This would lead to result[idx] being undefined, thus we need a sanity check here
+      if (result[idx]) {
+        result[idx].push(data[id]);
+      }
     }
   });
 

ee/spec/frontend/analytics/productivity_analytics/utils_spec.js

@@ -93,6 +93,26 @@ describe('Productivity Analytics utils', () => {
       ];
       expect(result).toEqual(expected);
     });
+
+    describe('when a data item is out of the start/end date range', () => {
+      it('ensures that the sanity check is performed', () => {
+        const startDate = new Date('2021-04-30');
+        const endDate = new Date('2021-05-02');
+
+        const data = {
+          1: { merged_at: '2021-04-29T16:28:57.078Z', metric: 10 }, // this item is before the startDate
+          2: { merged_at: '2021-04-30T09:44:22.012Z', metric: 20 },
+          3: { merged_at: '2021-05-02T23:09:31.715Z', metric: 40 },
+        };
+        const result = transformScatterData(data, startDate, endDate);
+        const expected = [
+          [{ merged_at: '2021-04-30T09:44:22.012Z', metric: 20 }],
+          [],
+          [{ merged_at: '2021-05-02T23:09:31.715Z', metric: 40 }],
+        ];
+        expect(result).toEqual(expected);
+      });
+    });
   });
 
   describe('getScatterPlotData', () => {