From f780db907d1071b5dda74b7cb7e4f6f539b40864 Mon Sep 17 00:00:00 2001
From: Maddy <12754347+MaddyDev@users.noreply.github.com>
Date: Tue, 21 Jul 2020 10:10:35 -0700
Subject: [PATCH] fix (#11437)

---
 extensions/notebook/src/book/bookTreeView.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/extensions/notebook/src/book/bookTreeView.ts b/extensions/notebook/src/book/bookTreeView.ts
index 40c23e7dad..d1854fc3bf 100644
--- a/extensions/notebook/src/book/bookTreeView.ts
+++ b/extensions/notebook/src/book/bookTreeView.ts
@@ -243,7 +243,7 @@ export class BookTreeViewProvider implements vscode.TreeDataProvider<BookTreeIte
 			notebookPath = uri.fsPath;
 		}
 
-		if (shouldReveal || this._bookViewer.visible) {
+		if (shouldReveal || this._bookViewer?.visible) {
 			bookItem = notebookPath ? await this.findAndExpandParentNode(notebookPath) : undefined;
 			// Select + focus item in viewlet if books viewlet is already open, or if we pass in variable
 			if (bookItem) {
@@ -264,7 +264,7 @@ export class BookTreeViewProvider implements vscode.TreeDataProvider<BookTreeIte
 			let book = allNodes ? Array.from(allNodes?.keys())?.filter(x => x.indexOf(notebookPath.substring(0, notebookPath.lastIndexOf(path.sep))) > -1) : undefined;
 			let bookNode = book?.length > 0 ? this.currentBook?.getNotebook(book.find(x => x.substring(0, x.lastIndexOf(path.sep)) === notebookPath.substring(0, notebookPath.lastIndexOf(path.sep)))) : undefined;
 			if (bookNode) {
-				if (this._bookViewer.visible) {
+				if (this._bookViewer?.visible) {
 					await this._bookViewer.reveal(bookNode, { select: true, focus: false, expand: 3 });
 				} else {
 					await this.getChildren(bookNode);