From a8cd39889db24fb0fb3bc8ba3dd239c282b67c2d Mon Sep 17 00:00:00 2001
From: "Gregory.Shrago" <gregory.shrago@jetbrains.com>
Date: Mon, 18 May 2015 22:51:22 +0300
Subject: [PATCH] handle null roots

---
 .../util/containers/TreeTraverser.java        | 24 ++++++++++++-------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/platform/util/src/com/intellij/util/containers/TreeTraverser.java b/platform/util/src/com/intellij/util/containers/TreeTraverser.java
index 9d1bb06db8d1..0dcd5b5bee6f 100644
--- a/platform/util/src/com/intellij/util/containers/TreeTraverser.java
+++ b/platform/util/src/com/intellij/util/containers/TreeTraverser.java
@@ -66,7 +66,7 @@ public abstract class TreeTraverser<T> {
    * iteration is in progress or when the iterators generated by {@link #children} are advanced.
    */
   @NotNull
-  public final JBIterable<T> preOrderTraversal(@NotNull final T root) {
+  public final JBIterable<T> preOrderTraversal(@Nullable final T root) {
     return new JBIterable<T>() {
       @Override
       public Iterator<T> iterator() {
@@ -96,7 +96,7 @@ public abstract class TreeTraverser<T> {
    * iteration is in progress or when the iterators generated by {@link #children} are advanced.
    */
   @NotNull
-  public final JBIterable<T> postOrderTraversal(@NotNull final T root) {
+  public final JBIterable<T> postOrderTraversal(@Nullable final T root) {
     return new JBIterable<T>() {
       @Override
       public Iterator<T> iterator() {
@@ -113,7 +113,7 @@ public abstract class TreeTraverser<T> {
    * iteration is in progress or when the iterators generated by {@link #children} are advanced.
    */
   @NotNull
-  public final JBIterable<T> breadthFirstTraversal(@NotNull final T root) {
+  public final JBIterable<T> breadthFirstTraversal(@Nullable final T root) {
     return new JBIterable<T>() {
       @Override
       public Iterator<T> iterator() {
@@ -172,8 +172,10 @@ public abstract class TreeTraverser<T> {
 
     int doneCount;
 
-    PreOrderIterator(@NotNull T root) {
-      stack.addLast(Pair.<T, Iterator<T>>create(null, new SingletonIterator<T>(root)));
+    PreOrderIterator(@Nullable T root) {
+      if (root != null) {
+        stack.addLast(Pair.<T, Iterator<T>>create(null, new SingletonIterator<T>(root)));
+      }
     }
 
     PreOrderIterator(@NotNull Iterable<T> roots) {
@@ -206,8 +208,10 @@ public abstract class TreeTraverser<T> {
 
   private final class PostOrderIterator extends DfsIterator<T> {
 
-    PostOrderIterator(T root) {
-      stack.addLast(Pair.create(root, children(root).iterator()));
+    PostOrderIterator(@Nullable T root) {
+      if (root != null) {
+        stack.addLast(Pair.create(root, children(root).iterator()));
+      }
     }
 
     @Override
@@ -230,8 +234,10 @@ public abstract class TreeTraverser<T> {
   private final class BreadthFirstIterator extends Itr<T> {
     final Deque<T> queue = new ArrayDeque<T>();
 
-    BreadthFirstIterator(@NotNull T root) {
-      queue.add(root);
+    BreadthFirstIterator(@Nullable T root) {
+      if (root != null) {
+        queue.add(root);
+      }
     }
 
     @Override