From b9f72a001bca4772a003248595ad20b13a5b2277 Mon Sep 17 00:00:00 2001
From: Bruce Wells <bruce.wells@simparel.com>
Date: Wed, 24 Oct 2018 14:16:11 -0400
Subject: Additional validation for bad expressions (*+ for example)

---
 src/NXP/Classes/Token/TokenMinus.php | 10 ++++++++++
 1 file changed, 10 insertions(+)

(limited to 'src/NXP/Classes/Token/TokenMinus.php')

diff --git a/src/NXP/Classes/Token/TokenMinus.php b/src/NXP/Classes/Token/TokenMinus.php
index 0463d4c..566c950 100644
--- a/src/NXP/Classes/Token/TokenMinus.php
+++ b/src/NXP/Classes/Token/TokenMinus.php
@@ -10,6 +10,8 @@
 
 namespace NXP\Classes\Token;
 
+use NXP\Exception\IncorrectExpressionException;
+
 /**
 * @author Alexander Kiryukhin <alexander@symdev.org>
 */
@@ -41,12 +43,20 @@ class TokenMinus extends AbstractOperator
 
     /**
      * @param InterfaceToken[] $stack
+     *
      * @return $this
+     *
+     * @throws \NXP\Exception\IncorrectExpressionException
      */
     public function execute(&$stack)
     {
         $op2 = array_pop($stack);
         $op1 = array_pop($stack);
+
+        if ($op1 === null || $op2 === null) {
+            throw new IncorrectExpressionException("Subtraction requires two operators");
+        }
+
         $result = $op1->getValue() - $op2->getValue();
 
         return new TokenNumber($result);
-- 
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