From f0056ef8dc9d7ffbd847843d426088a1747ff526 Mon Sep 17 00:00:00 2001
From: valis <valery.isaev@gmail.com>
Date: Wed, 22 May 2024 13:33:43 +0300
Subject: [PATCH] Fix a NPE

---
 .../java/org/arend/term/concrete/ConcreteCompareVisitor.java     | 1 +
 1 file changed, 1 insertion(+)

diff --git a/base/src/main/java/org/arend/term/concrete/ConcreteCompareVisitor.java b/base/src/main/java/org/arend/term/concrete/ConcreteCompareVisitor.java
index 91403dcb4..a0a394fe1 100644
--- a/base/src/main/java/org/arend/term/concrete/ConcreteCompareVisitor.java
+++ b/base/src/main/java/org/arend/term/concrete/ConcreteCompareVisitor.java
@@ -57,6 +57,7 @@ public Boolean visitReference(Concrete.ReferenceExpression expr1, Concrete.Expre
 
   private boolean compareLevels(List<Concrete.LevelExpression> levels1, List<Concrete.LevelExpression> levels2) {
     if (levels1 == null) return levels2 == null;
+    if (levels2 == null) return false;
     if (levels1.size() != levels2.size()) return false;
     for (int i = 0; i < levels1.size(); i++) {
       if (!compareLevel(levels1.get(i), levels2.get(i))) return false;