diff --git a/platform/platform-impl/src/com/intellij/ui/tree/AbstractTreeWalker.java b/platform/platform-impl/src/com/intellij/ui/tree/AbstractTreeWalker.java
index ffccdae9f12c..b128d1a2c151 100644
--- a/platform/platform-impl/src/com/intellij/ui/tree/AbstractTreeWalker.java
+++ b/platform/platform-impl/src/com/intellij/ui/tree/AbstractTreeWalker.java
@@ -8,7 +8,6 @@ import org.jetbrains.concurrency.Promise;
 import javax.swing.tree.TreePath;
 import java.util.ArrayDeque;
 import java.util.Collection;
-import java.util.Deque;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Function;
 
@@ -17,7 +16,7 @@ public abstract class AbstractTreeWalker<N> {
 
   private final AtomicReference<State> state = new AtomicReference<>();
   private final AsyncPromise<TreePath> promise = new AsyncPromise<>();
-  private final Deque<ArrayDeque<N>> stack = new ArrayDeque<>();
+  private final ArrayDeque<ArrayDeque<N>> stack = new ArrayDeque<>();
   private final Function<? super N, Object> converter;
   private final TreeVisitor visitor;
   private volatile TreePath current;
diff --git a/platform/platform-impl/src/com/intellij/ui/tree/StructureTreeModel.java b/platform/platform-impl/src/com/intellij/ui/tree/StructureTreeModel.java
index 646d130314ed..d5a31749a4eb 100644
--- a/platform/platform-impl/src/com/intellij/ui/tree/StructureTreeModel.java
+++ b/platform/platform-impl/src/com/intellij/ui/tree/StructureTreeModel.java
@@ -20,7 +20,9 @@ import javax.swing.tree.TreeNode;
 import javax.swing.tree.TreePath;
 import java.util.*;
 
-import static java.util.Collections.*;
+import static java.util.Collections.emptyList;
+import static java.util.Collections.enumeration;
+import static java.util.Collections.unmodifiableList;
 
 /**
  * @author Sergey.Malenkov
@@ -38,13 +40,25 @@ public class StructureTreeModel extends AbstractTreeModel implements Disposable,
               : new Invoker.EDT(this);
   }
 
-  public final void setComparator(@NotNull Comparator<? super NodeDescriptor> comparator) {
+  /**
+   * @param comparator a comparator to sort tree nodes or {@code null} to disable sorting
+   */
+  public final void setComparator(@Nullable Comparator<? super NodeDescriptor> comparator) {
     if (disposed) return;
-    this.comparator = (node1, node2) -> comparator.compare(node1.getDescriptor(), node2.getDescriptor());
-    invalidate();
+    if (comparator != null) {
+      this.comparator = (node1, node2) -> comparator.compare(node1.getDescriptor(), node2.getDescriptor());
+      invalidate();
+    }
+    else if (this.comparator != null) {
+      this.comparator = null;
+      invalidate();
+    }
   }
 
-  public void setStructure(@NotNull AbstractTreeStructure structure) {
+  /**
+   * @param structure a structure to build tree model or {@code null} to clear its content
+   */
+  public void setStructure(@Nullable AbstractTreeStructure structure) {
     if (disposed) return;
     this.structure = structure;
     invalidate();
diff --git a/platform/platform-impl/src/com/intellij/ui/tree/project/ProjectFileNodeUpdater.java b/platform/platform-impl/src/com/intellij/ui/tree/project/ProjectFileNodeUpdater.java
index cc72baa6d399..5f17dcf9dcc3 100644
--- a/platform/platform-impl/src/com/intellij/ui/tree/project/ProjectFileNodeUpdater.java
+++ b/platform/platform-impl/src/com/intellij/ui/tree/project/ProjectFileNodeUpdater.java
@@ -109,7 +109,7 @@ public abstract class ProjectFileNodeUpdater {
 
   /**
    * Notifies that project roots are changed.
-   * The {@link #update} method will be executed with a small delay
+   * The {@link #onInvokerThread} method will be executed with a small delay
    * after calling of this method.
    *
    * @see #getUpdatingDelay
@@ -120,7 +120,7 @@ public abstract class ProjectFileNodeUpdater {
 
   /**
    * Notifies that the specified file (or folder) is changed.
-   * The {@link #update} method will be executed with a small delay
+   * The {@link #onInvokerThread} method will be executed with a small delay
    * after last calling of this method,
    * i.e. a bunch of modified files will be reported together.
    *
@@ -152,7 +152,7 @@ public abstract class ProjectFileNodeUpdater {
   }
 
   /**
-   * @return a delay between an event and the {@link #update} method calling,
+   * @return a delay between an event and the {@link #onInvokerThread} method calling,
    * that is used to collect a bunch of changes
    */
   protected int getUpdatingDelay() {
@@ -220,7 +220,8 @@ public abstract class ProjectFileNodeUpdater {
 
   /**
    * This method is called on invoker's thread to report changes in virtual files.
-   *  @param fromRoot     {@code true} if roots are changed
+   *
+   * @param fromRoot     {@code true} if roots are changed
    * @param updatedFiles a set of modified files
    */
   protected abstract void updateStructure(boolean fromRoot, @NotNull Set<? extends VirtualFile> updatedFiles);
diff --git a/platform/util/src/com/intellij/util/ui/tree/TreeModelListenerList.java b/platform/util/src/com/intellij/util/ui/tree/TreeModelListenerList.java
index 7a2a7182f95b..4aed1b082143 100644
--- a/platform/util/src/com/intellij/util/ui/tree/TreeModelListenerList.java
+++ b/platform/util/src/com/intellij/util/ui/tree/TreeModelListenerList.java
@@ -20,14 +20,13 @@ import org.jetbrains.annotations.NotNull;
 import javax.swing.event.TreeModelEvent;
 import javax.swing.event.TreeModelListener;
 import java.util.ArrayDeque;
-import java.util.Deque;
 
 /**
  * @author Sergey.Malenkov
  */
 public final class TreeModelListenerList implements TreeModelListener {
   private static final TreeModelListener[] EMPTY_ARRAY = new TreeModelListener[0];
-  private final Deque<TreeModelListener> myDeque = new ArrayDeque<TreeModelListener>();
+  private final ArrayDeque<TreeModelListener> myDeque = new ArrayDeque<TreeModelListener>();
   private volatile boolean myDequeEmpty = true;
 
   /**
@@ -50,9 +49,11 @@ public final class TreeModelListenerList implements TreeModelListener {
    * @param listener a listener to remove
    */
   public void remove(@NotNull TreeModelListener listener) {
-    synchronized (myDeque) {
-      myDeque.remove(listener);
-      myDequeEmpty = myDeque.isEmpty();
+    if (!myDequeEmpty) {
+      synchronized (myDeque) {
+        myDeque.remove(listener);
+        myDequeEmpty = myDeque.isEmpty();
+      }
     }
   }
 
@@ -61,9 +62,11 @@ public final class TreeModelListenerList implements TreeModelListener {
    * This method is safe for use by multiple concurrent threads.
    */
   public void clear() {
-    synchronized (myDeque) {
-      myDeque.clear();
-      myDequeEmpty = true;
+    if (!myDequeEmpty) {
+      synchronized (myDeque) {
+        myDeque.clear();
+        myDequeEmpty = true;
+      }
     }
   }