From f7d4d01bc822d3edb1302e62f29833fc675c78cd Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Wed, 26 Jul 2017 13:25:12 -0700
Subject: [PATCH] Correctly handle invalid strings.

---
 src/org/nwapw/abacus/tree/TreeNode.java | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/org/nwapw/abacus/tree/TreeNode.java b/src/org/nwapw/abacus/tree/TreeNode.java
index 45f7741..8540677 100644
--- a/src/org/nwapw/abacus/tree/TreeNode.java
+++ b/src/org/nwapw/abacus/tree/TreeNode.java
@@ -129,7 +129,9 @@ public abstract class TreeNode {
      * @return the resulting tree.
      */
     public static TreeNode fromString(String string){
-        ArrayList<Match<TokenType>> matches = intoPostfix(string, tokenize(string));
+        ArrayList<Match<TokenType>> matches = tokenize(string);
+        if(matches == null) return null;
+        matches = intoPostfix(string, matches);
         if(matches == null) return null;
 
         Collections.reverse(matches);