Fix Store.getFieldValues() to include null values in returned set (#4307)

Previously, `getFieldValues()` silently excluded null/undefined values, preventing grid column filters from offering a [blank] option. Inverted the nil check so null is added to the result set.

Author: jskupsik

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## 82.0.4 - 2026-03-23
+
+### 🐞 Bug Fixes
+
+* Fixed `Store.getFieldValues()` to include `null` in its returned set when records contain
+  null/undefined values. Previously these were silently excluded, preventing grid column filters
+  from offering a [blank] option.
+
 ## 82.0.3 - 2026-03-02
 
 ### 🐞 Bug Fixes

data/Store.ts

@@ -849,12 +849,12 @@ export class Store
         const ret = new Set();
         recs.forEach(rec => {
             const val = rec.get(fieldName);
-            if (!isNil(val)) {
-                if (field.type === 'tags') {
-                    val.forEach(it => ret.add(it));
-                } else {
-                    ret.add(val);
-                }
+            if (isNil(val)) {
+                ret.add(null);
+            } else if (field.type === 'tags') {
+                val.forEach(it => ret.add(it));
+            } else {
+                ret.add(val);
             }
         });