fix strict null checks

src/vs/base/browser/ui/tree/abstractTree.ts

@@ -202,13 +202,13 @@ function asTreeEvent<T>(event: IListEvent<ITreeNode<T, any>>): ITreeEvent<T> {
 function asTreeMouseEvent<T>(event: IListMouseEvent<ITreeNode<T, any>>): ITreeMouseEvent<T> {
 	return {
 		browserEvent: event.browserEvent,
-		element: event.element.element
+		element: event.element && event.element.element
 	};
 }
 
 function asTreeContextMenuEvent<T>(event: IListContextMenuEvent<ITreeNode<T, any>>): ITreeContextMenuEvent<T> {
 	return {
-		element: event.element.element,
+		element: event.element && event.element.element,
 		browserEvent: event.browserEvent,
 		anchor: event.anchor
 	};

src/vs/base/browser/ui/tree/dataTree.ts

@@ -92,21 +92,21 @@ class DataTreeRenderer<T, TFilterData, TTemplateData> implements ITreeRenderer<I
 function asTreeEvent<T>(e: ITreeEvent<IDataTreeNode<T>>): ITreeEvent<T> {
 	return {
 		browserEvent: e.browserEvent,
-		elements: e.elements.map(e => e.element)
+		elements: e.elements.map(e => e.element!)
 	};
 }
 
 function asTreeMouseEvent<T>(e: ITreeMouseEvent<IDataTreeNode<T>>): ITreeMouseEvent<T> {
 	return {
 		browserEvent: e.browserEvent,
-		element: e.element.element
+		element: e.element && e.element.element!
 	};
 }
 
 function asTreeContextMenuEvent<T>(e: ITreeContextMenuEvent<IDataTreeNode<T>>): ITreeContextMenuEvent<T> {
 	return {
 		browserEvent: e.browserEvent,
-		element: e.element.element,
+		element: e.element && e.element.element!,
 		anchor: e.anchor
 	};
 }