[v9.2.x] Alerting: Fix folder picker clear action (#56915)

Co-authored-by: Konrad Lalik <konrad.lalik@grafana.com>

.gitignore

@@ -61,6 +61,7 @@ public/css/*.min.css
 *.sublime-workspace
 *.swp
 .idea/
+.fleet/
 *.iml
 *.tmp
 .DS_Store

public/app/core/components/Select/FolderPicker.tsx

@@ -193,9 +193,8 @@ export function FolderPicker(props: Props) {
   }, [folder]);
 
   const onFolderChange = useCallback(
-    (newFolder: SelectableValue<number>, actionMeta: ActionMeta) => {
-      const value = newFolder.value;
-      if (value === VALUE_FOR_ADD) {
+    (newFolder: SelectableValue<number> | null | undefined, actionMeta: ActionMeta) => {
+      if (newFolder?.value === VALUE_FOR_ADD) {
         setFolder({
           id: VALUE_FOR_ADD,
           title: inputValue,

public/app/plugins/panel/alertlist/module.tsx

@@ -246,7 +246,7 @@ const unifiedAlertList = new PanelPlugin<UnifiedAlertListOptions>(UnifiedAlertLi
     .addCustomEditor({
       path: 'folder',
       name: 'Folder',
-      description: 'Filter for alerts in the selected folder',
+      description: 'Filter for alerts in the selected folder (only for Grafana alerts)',
       id: 'folder',
       defaultValue: null,
       editor: function RenderFolderPicker(props) {
@@ -279,7 +279,7 @@ const unifiedAlertList = new PanelPlugin<UnifiedAlertListOptions>(UnifiedAlertLi
             noDefault
             current={props.value}
             onChange={(ds) => props.onChange(ds.name)}
-            onClear={() => props.onChange('')}
+            onClear={() => props.onChange(null)}
           />
         );
       },