diff --git a/java/java-psi-impl/src/com/intellij/psi/impl/source/tree/JavaTreeGenerator.java b/java/java-psi-impl/src/com/intellij/psi/impl/source/tree/JavaTreeGenerator.java
index b5ca2ea117c3..b0ae2ef73af8 100644
--- a/java/java-psi-impl/src/com/intellij/psi/impl/source/tree/JavaTreeGenerator.java
+++ b/java/java-psi-impl/src/com/intellij/psi/impl/source/tree/JavaTreeGenerator.java
@@ -49,7 +49,7 @@ public class JavaTreeGenerator implements TreeGenerator {
 
   @Override
   @Nullable
-  public TreeElement generateTreeFor(PsiElement original, final CharTable table, final PsiManager manager) {
+  public TreeElement generateTreeFor(@NotNull PsiElement original, @NotNull final CharTable table, @NotNull final PsiManager manager) {
     if (original instanceof PsiKeyword || original instanceof PsiIdentifier) {
       final String text = original.getText();
       return createLeafFromText(text, table, manager, original, ((PsiJavaToken)original).getTokenType());
diff --git a/platform/core-impl/src/com/intellij/psi/impl/source/tree/ChangeUtil.java b/platform/core-impl/src/com/intellij/psi/impl/source/tree/ChangeUtil.java
index 56e01ca4fa8d..13ca96e9df26 100644
--- a/platform/core-impl/src/com/intellij/psi/impl/source/tree/ChangeUtil.java
+++ b/platform/core-impl/src/com/intellij/psi/impl/source/tree/ChangeUtil.java
@@ -144,7 +144,8 @@ public class ChangeUtil {
   }
 
   @Nullable
-  public static TreeElement generateTreeElement(PsiElement original, CharTable table, final PsiManager manager) {
+  public static TreeElement generateTreeElement(@Nullable PsiElement original, @NotNull CharTable table, @NotNull final PsiManager manager) {
+    if (original == null) return null;
     PsiUtilCore.ensureValid(original);
     if (SourceTreeToPsiMap.hasTreeElement(original)) {
       return copyElement((TreeElement)SourceTreeToPsiMap.psiElementToTree(original), table);
diff --git a/platform/core-impl/src/com/intellij/psi/impl/source/tree/TreeGenerator.java b/platform/core-impl/src/com/intellij/psi/impl/source/tree/TreeGenerator.java
index c6528ba7aeb3..20f27f3d5a39 100644
--- a/platform/core-impl/src/com/intellij/psi/impl/source/tree/TreeGenerator.java
+++ b/platform/core-impl/src/com/intellij/psi/impl/source/tree/TreeGenerator.java
@@ -23,11 +23,12 @@ import com.intellij.openapi.extensions.ExtensionPointName;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiManager;
 import com.intellij.util.CharTable;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 public interface TreeGenerator {
   ExtensionPointName<TreeGenerator> EP_NAME = ExtensionPointName.create("com.intellij.treeGenerator");
   
   @Nullable
-  TreeElement generateTreeFor(PsiElement original, CharTable table, final PsiManager manager);
+  TreeElement generateTreeFor(@NotNull PsiElement original, @NotNull CharTable table, @NotNull final PsiManager manager);
 }
\ No newline at end of file
diff --git a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/source/impl/GroovyTreeGenerator.java b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/source/impl/GroovyTreeGenerator.java
index c1a08cc3a593..97d48f1229fc 100644
--- a/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/source/impl/GroovyTreeGenerator.java
+++ b/plugins/groovy/groovy-psi/src/org/jetbrains/plugins/groovy/lang/psi/impl/source/impl/GroovyTreeGenerator.java
@@ -20,12 +20,13 @@ import com.intellij.psi.PsiManager;
 import com.intellij.psi.impl.source.tree.TreeElement;
 import com.intellij.psi.impl.source.tree.TreeGenerator;
 import com.intellij.util.CharTable;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.plugins.groovy.lang.psi.GroovyPsiElementFactory;
 import org.jetbrains.plugins.groovy.lang.psi.api.auxiliary.modifiers.GrModifierList;
 
 public class GroovyTreeGenerator implements TreeGenerator {
   @Override
-  public TreeElement generateTreeFor(PsiElement original, CharTable table, PsiManager manager) {
+  public TreeElement generateTreeFor(@NotNull PsiElement original, @NotNull CharTable table, @NotNull PsiManager manager) {
 
     if (original instanceof GrModifierList) {
       final String text = original.getText();