From 9eefd13615922bccf999bcc775af7da3bf51526f Mon Sep 17 00:00:00 2001
From: Oleksii Trekhleb <trehleb@gmail.com>
Date: Fri, 6 Apr 2018 07:01:16 +0300
Subject: [PATCH] Fix binary tree node.

---
 src/data-structures/tree/BinaryTreeNode.js     |  8 ++++++--
 .../tree/__test__/BinaryTreeNode.test.js       | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/data-structures/tree/BinaryTreeNode.js b/src/data-structures/tree/BinaryTreeNode.js
index 5498b9d6..cca840da 100644
--- a/src/data-structures/tree/BinaryTreeNode.js
+++ b/src/data-structures/tree/BinaryTreeNode.js
@@ -32,13 +32,17 @@ export default class BinaryTreeNode {
 
   setLeft(node) {
     this.left = node;
-    this.left.parent = this;
+    if (node) {
+      this.left.parent = this;
+    }
     return this;
   }
 
   setRight(node) {
     this.right = node;
-    this.right.parent = this;
+    if (node) {
+      this.right.parent = this;
+    }
     return this;
   }
 
diff --git a/src/data-structures/tree/__test__/BinaryTreeNode.test.js b/src/data-structures/tree/__test__/BinaryTreeNode.test.js
index c32123a1..9160a965 100644
--- a/src/data-structures/tree/__test__/BinaryTreeNode.test.js
+++ b/src/data-structures/tree/__test__/BinaryTreeNode.test.js
@@ -155,4 +155,22 @@ describe('BinaryTreeNode', () => {
     expect(right.height).toBe(0);
     expect(root.balanceFactor).toBe(-1);
   });
+
+  it('should set null for left and right node', () => {
+    const root = new BinaryTreeNode(2);
+    const left = new BinaryTreeNode(1);
+    const right = new BinaryTreeNode(3);
+
+    root.setLeft(left);
+    root.setRight(right);
+
+    expect(root.left.value).toBe(1);
+    expect(root.right.value).toBe(3);
+
+    root.setLeft(null);
+    root.setRight(null);
+
+    expect(root.left).toBeNull();
+    expect(root.right).toBeNull();
+  });
 });