fix(DetailsList): DetailsRow correctly falls back to horizontal FocusZone (microsoft#35180)

Author: smhigley

change/@fluentui-react-d23e2624-d5ec-4f8a-a317-1c7b9d11141e.json

@@ -0,0 +1,7 @@
+{
+  "type": "patch",
+  "comment": "fix(DetailsList): DetailsRow correctly falls back to horizontal FocusZone",
+  "packageName": "@fluentui/react",
+  "email": "[email protected]",
+  "dependentChangeType": "patch"
+}

packages/react/src/components/DetailsList/DetailsRow.base.tsx

@@ -226,7 +226,7 @@ export class DetailsRowBase extends React.Component<IDetailsRowBaseProps, IDetai
     const ariaSelected = selectionMode === SelectionMode.none ? undefined : isSelected;
     const ariaPositionInSet = group ? itemIndex - group.startIndex + 1 : undefined;
     const ariaSetSize = group ? group.count : undefined;
-    const focusZoneDirection = focusZoneProps ? focusZoneProps.direction : FocusZoneDirection.horizontal;
+    const focusZoneDirection = focusZoneProps?.direction ?? FocusZoneDirection.horizontal;
 
     this._classNames = {
       ...this._classNames,