fix(client-core): preserve zero values with fillWithValue in pivot (#10225)

The fillWithValue pivot config option was using the || (logical OR) operator,
which treats 0 as falsy. This caused actual zero values in the data to be
incorrectly replaced by fillWithValue, not just missing/undefined values.

Changed the implementation to use the ?? (nullish coalescing) operator instead,
which only falls through for null and undefined values, preserving actual 0
values in the data.

Impact: Users can now use fillWithValue to display 'no data' indicators (like
'-' or 'N/A') without also replacing legitimate zeros in their data.

Fixes #10225

Author: Debjit Mandal

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

@@ -535,8 +535,7 @@ export default class ResultSet<T extends Record<string, any> = any> {
 
     const pivotImpl = (resultIndex = 0) => {
       let groupByXAxis = groupByToPairs<{ xValues: string[], row: Record<string, any> }, string>(({ xValues }) => this.axisValuesString(xValues));
-
-      const measureValue = (row: Record<string, any>, measure: string) => row[measure] || normalizedPivotConfig.fillWithValue || 0;
+      const measureValue = (row: Record<string, any>, measure: string) => row[measure] ?? normalizedPivotConfig.fillWithValue ?? 0;
 
       if (
         normalizedPivotConfig.fillMissingDates &&

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

@@ -1694,6 +1694,79 @@ describe('ResultSet', () => {
       ]);
     });
 
+    test('fillWithValue should preserve actual zero values (issue #10225)', () => {
+      const resultSet = new ResultSet({
+        query: {
+          measures: ['TestCube.value'],
+          dimensions: ['TestCube.category', 'TestCube.type'],
+          filters: [],
+          timezone: 'UTC'
+        },
+        data: [
+          {
+            'TestCube.category': 'A',
+            'TestCube.type': 'X',
+            'TestCube.value': 10
+          },
+          {
+            'TestCube.category': 'A',
+            'TestCube.type': 'Y',
+            'TestCube.value': 0
+          },
+          {
+            'TestCube.category': 'B',
+            'TestCube.type': 'X',
+            'TestCube.value': 30
+          }
+        ],
+        annotation: {
+          measures: {
+            'TestCube.value': {
+              title: 'Value',
+              shortTitle: 'Value',
+              type: 'number'
+            }
+          },
+          dimensions: {
+            'TestCube.category': {
+              title: 'Category',
+              shortTitle: 'Category',
+              type: 'string'
+            },
+            'TestCube.type': {
+              title: 'Type',
+              shortTitle: 'Type',
+              type: 'string'
+            }
+          },
+          segments: {},
+          timeDimensions: {}
+        }
+      } as any);
+
+      const pivotConfig = {
+        x: ['TestCube.category'],
+        y: ['TestCube.type', 'measures'],
+        fillWithValue: '-'
+      };
+
+      const result = resultSet.tablePivot(pivotConfig);
+
+      // Actual zero values should be preserved, not replaced by fillWithValue
+      expect(result).toEqual([
+        {
+          'TestCube.category': 'A',
+          'X,TestCube.value': 10,
+          'Y,TestCube.value': 0 // Zero should be preserved, not replaced with '-'
+        },
+        {
+          'TestCube.category': 'B',
+          'X,TestCube.value': 30,
+          'Y,TestCube.value': '-' // Missing value should be replaced with '-'
+        }
+      ]);
+    });
+
     test('same dimension and time dimension without granularity', () => {
       const resultSet = new ResultSet({
         query: {