diff --git a/java/openapi/src/com/intellij/codeInsight/NullableNotNullManager.java b/java/openapi/src/com/intellij/codeInsight/NullableNotNullManager.java
index ab1324b1f0a2..85c3adb9009d 100644
--- a/java/openapi/src/com/intellij/codeInsight/NullableNotNullManager.java
+++ b/java/openapi/src/com/intellij/codeInsight/NullableNotNullManager.java
@@ -65,6 +65,7 @@ public class NullableNotNullManager implements PersistentStateComponent<Element>
 
   private static void addAllIfNotPresent(Collection<String> collection, String... annotations) {
     for (String annotation : annotations) {
+      LOG.assertTrue(annotation != null);
       if (!collection.contains(annotation)) {
         collection.add(annotation);
       }