fix(ag-grid): persist "None" value aggregation selection (#41386)

Co-authored-by: Enzo Martellucci <52219496+EnxDev@users.noreply.github.com>
Co-authored-by: Enzo Martellucci <enzomartellucci@gmail.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit fb496e158a)

superset-frontend/plugins/plugin-chart-ag-grid-table/test/utils/getColumnStateSignature.test.ts

@@ -0,0 +1,82 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+import type { ColumnState } from '@superset-ui/core/components/ThemedAgGridReact';
+import getColumnStateSignature from '../../src/utils/getColumnStateSignature';
+
+const filterModel = {};
+
+test('signature changes when a column value aggregation changes', () => {
+  const before = getColumnStateSignature(
+    [{ colId: 'sales', aggFunc: 'sum' }],
+    [],
+    filterModel,
+  );
+  const after = getColumnStateSignature(
+    [{ colId: 'sales', aggFunc: 'avg' }],
+    [],
+    filterModel,
+  );
+  expect(after).not.toEqual(before);
+});
+
+test('switching value aggregation to "None" (null/undefined) changes the signature', () => {
+  // Regression #107166: "None" must be captured so it persists on reload.
+  const sumState = getColumnStateSignature(
+    [{ colId: 'sales', aggFunc: 'sum' }],
+    [],
+    filterModel,
+  );
+  const noneNull = getColumnStateSignature(
+    [{ colId: 'sales', aggFunc: null }],
+    [],
+    filterModel,
+  );
+  const noneUndefined = getColumnStateSignature(
+    [{ colId: 'sales' }],
+    [],
+    filterModel,
+  );
+
+  expect(noneNull).not.toEqual(sumState);
+  expect(noneUndefined).not.toEqual(sumState);
+  // null and undefined both represent "None" and must be treated identically.
+  expect(noneNull).toEqual(noneUndefined);
+});
+
+test('signature is stable when nothing changes', () => {
+  const columnState: ColumnState[] = [{ colId: 'sales', aggFunc: 'sum' }];
+  const a = getColumnStateSignature(columnState, [], filterModel);
+  const b = getColumnStateSignature([...columnState], [], filterModel);
+  expect(a).toEqual(b);
+});
+
+test('a function aggFunc is distinguishable from "None"', () => {
+  // Pins the defensive marker: function aggFuncs stay distinct from "None".
+  const customAgg = getColumnStateSignature(
+    [{ colId: 'sales', aggFunc: () => 42 }],
+    [],
+    filterModel,
+  );
+  const none = getColumnStateSignature(
+    [{ colId: 'sales', aggFunc: null }],
+    [],
+    filterModel,
+  );
+  expect(customAgg).not.toEqual(none);
+});