fix(client-core): Remove default value in table pivot (#9869)

* Remove defaulting to empty string in tablePivot

* Added a regression test

Author: Emile-Filteau

packages/cubejs-client-core/src/ResultSet.ts

@@ -784,7 +784,7 @@ export default class ResultSet<T extends Record<string, any> = any> {
       [
         ...(normalizedPivotConfig.x).map((key, index): [string, string | number] => [
           key,
-          xValues[index] ?? ''
+          xValues[index]
         ]),
         ...(isMeasuresPresent
           ? yValuesArray.map(([yValues, measure]): [string, string | number] => [

packages/cubejs-client-core/test/ResultSet.test.ts

@@ -1807,5 +1807,28 @@ describe('ResultSet', () => {
         ]
       );
     });
+
+    test('keeps null values on non-matching rows', () => {
+      const resultSet = new ResultSet({
+        query: {
+          dimensions: [
+            'User.name',
+            'Friend.name'
+          ],
+        },
+        data: [
+          {
+            'User.name': 'Bob',
+            'Friend.name': null,
+          }
+        ],
+      } as any);
+
+      expect(resultSet.tablePivot()).toEqual(
+        [
+          { 'User.name': 'Bob', 'Friend.name': null },
+        ]
+      );
+    });
   });
 });