Fix 102-binary-tree-level-order-traversal.js empty array error

Author: thisiswhale

javascript/102-Binary-Tree-Level-Order-Traversal.js

@@ -12,6 +12,8 @@
  */
 var levelOrder = function(root) {
 
+    if(!root) return [];
+
     const result = [];
     const queue = [root];