1 files changed, 10 insertions, 0 deletions
diff --git a/src/NXP/Classes/Token/TokenPlus.php b/src/NXP/Classes/Token/TokenPlus.php
index f9562e7..fe5a1d6 100644
--- a/src/NXP/Classes/Token/TokenPlus.php
+++ b/src/NXP/Classes/Token/TokenPlus.php
@@ -10,6 +10,8 @@
 
 namespace NXP\Classes\Token;
 
+use NXP\Exception\IncorrectExpressionException;
+
 /**
 * @author Alexander Kiryukhin <alexander@symdev.org>
 */
@@ -41,12 +43,20 @@ class TokenPlus 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("Addition requires two operators");
+        }
+
         $result = $op1->getValue() + $op2->getValue();
 
         return new TokenNumber($result);