diff --git a/platform/lang-impl/src/com/intellij/util/PatternValuesIndex.java b/platform/lang-impl/src/com/intellij/util/PatternValuesIndex.java
index 26d39583a4df..599a0f15092b 100644
--- a/platform/lang-impl/src/com/intellij/util/PatternValuesIndex.java
+++ b/platform/lang-impl/src/com/intellij/util/PatternValuesIndex.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2010 JetBrains s.r.o.
+ * Copyright 2000-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 package com.intellij.util;
 
 import com.intellij.patterns.*;
+import com.intellij.util.containers.ContainerUtil;
 import gnu.trove.THashSet;
 
 import java.util.Collection;
@@ -49,7 +50,7 @@ public class PatternValuesIndex {
         final ElementPatternCondition<?> patternCondition = pattern.getCondition();
         final InitialPatternCondition<?> initialCondition = patternCondition.getInitialCondition();
         if (initialCondition instanceof InitialPatternConditionPlus) {
-          stack.addAll(((InitialPatternConditionPlus<?>)initialCondition).getPatterns());
+          ContainerUtil.addAllNotNull(stack, ((InitialPatternConditionPlus<?>)initialCondition).getPatterns());
         }
         for (PatternCondition<?> condition : patternCondition.getConditions()) {
           if (condition instanceof PatternConditionPlus) {