diff --git a/platform/lang-api/src/com/intellij/usageView/UsageInfo.java b/platform/lang-api/src/com/intellij/usageView/UsageInfo.java
index 719c0fe54db2..ba05ec7d7fc4 100644
--- a/platform/lang-api/src/com/intellij/usageView/UsageInfo.java
+++ b/platform/lang-api/src/com/intellij/usageView/UsageInfo.java
@@ -206,6 +206,7 @@ public class UsageInfo {
                                Math.min(range.getEndOffset(), range.getStartOffset() + rangeInElement.getEndOffset()));
   }
 
+  @NotNull
   public Project getProject() {
     return mySmartPointer.getProject();
   }
diff --git a/platform/usageView/src/com/intellij/usages/rules/MergeableUsage.java b/platform/usageView/src/com/intellij/usages/rules/MergeableUsage.java
index da596ec2a9c6..92de88c2ff0d 100644
--- a/platform/usageView/src/com/intellij/usages/rules/MergeableUsage.java
+++ b/platform/usageView/src/com/intellij/usages/rules/MergeableUsage.java
@@ -15,6 +15,8 @@
  */
 package com.intellij.usages.rules;
 
+import org.jetbrains.annotations.NotNull;
+
 /**
  * @author max
  */
@@ -23,7 +25,7 @@ public interface MergeableUsage {
    * @param mergeableUsage
    * @return true if merge succeeded
    */
-  boolean merge(MergeableUsage mergeableUsage);
+  boolean merge(@NotNull MergeableUsage mergeableUsage);
 
   /**
    * Revert to original status prior any merges