diff --git a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/evaluate/quick/XDebuggerInstanceTreeCreator.java b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/evaluate/quick/XDebuggerInstanceTreeCreator.java
index 49eb3845c505..496e8ea983db 100644
--- a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/evaluate/quick/XDebuggerInstanceTreeCreator.java
+++ b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/evaluate/quick/XDebuggerInstanceTreeCreator.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2015 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -58,12 +58,7 @@ public class XDebuggerInstanceTreeCreator implements DebuggerTreeCreator<Pair<XI
     final XValueNodeImpl root = new XValueNodeImpl(tree, null, descriptor.getSecond(),
                                                    new InstanceEvaluatorTreeRootValue(descriptor.getFirst(), descriptor.getSecond()));
     tree.setRoot(root, false);
-    Condition<TreeNode> visibleRootCondition = new Condition<TreeNode>() {
-      @Override
-      public boolean value(TreeNode node) {
-        return node.getParent() == root;
-      }
-    };
+    Condition<TreeNode> visibleRootCondition = node -> node.getParent() == root;
     tree.expandNodesOnLoad(visibleRootCondition);
     tree.selectNodeOnLoad(visibleRootCondition);
 
diff --git a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/evaluate/quick/XDebuggerTreeCreator.java b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/evaluate/quick/XDebuggerTreeCreator.java
index 14799efb59db..a9f39a6d92ab 100644
--- a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/evaluate/quick/XDebuggerTreeCreator.java
+++ b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/evaluate/quick/XDebuggerTreeCreator.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2015 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,7 +17,6 @@ package com.intellij.xdebugger.impl.evaluate.quick;
 
 import com.intellij.concurrency.ResultConsumer;
 import com.intellij.openapi.project.Project;
-import com.intellij.openapi.util.Condition;
 import com.intellij.openapi.util.Pair;
 import com.intellij.ui.treeStructure.Tree;
 import com.intellij.xdebugger.XSourcePosition;
@@ -30,8 +29,6 @@ import com.intellij.xdebugger.impl.ui.tree.XDebuggerTree;
 import com.intellij.xdebugger.impl.ui.tree.nodes.XValueNodeImpl;
 import org.jetbrains.annotations.NotNull;
 
-import javax.swing.tree.TreeNode;
-
 public class XDebuggerTreeCreator implements DebuggerTreeCreator<Pair<XValue,String>> {
   @NotNull private final Project myProject;
   private final XDebuggerEditorsProvider myProvider;
@@ -54,12 +51,7 @@ public class XDebuggerTreeCreator implements DebuggerTreeCreator<Pair<XValue,Str
     tree.setRoot(root, true);
     tree.setSelectionRow(0);
     // expand root on load
-    tree.expandNodesOnLoad(new Condition<TreeNode>() {
-      @Override
-      public boolean value(TreeNode node) {
-        return node == root;
-      }
-    });
+    tree.expandNodesOnLoad(node -> node == root);
     return tree;
   }
 
diff --git a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/frame/XWatchesViewImpl.java b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/frame/XWatchesViewImpl.java
index 608c71d08e66..1386f7750f93 100644
--- a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/frame/XWatchesViewImpl.java
+++ b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/frame/XWatchesViewImpl.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2015 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -386,22 +386,20 @@ public class XWatchesViewImpl extends XVariablesView implements DnDNativeTarget,
   public void removeWatches(List<? extends XDebuggerTreeNode> nodes) {
     List<? extends WatchNode> children = myRootNode.getWatchChildren();
     int minIndex = Integer.MAX_VALUE;
-    List<XDebuggerTreeNode> toRemove = new ArrayList<XDebuggerTreeNode>();
-    if (children != null) {
-      for (XDebuggerTreeNode node : nodes) {
-        @SuppressWarnings("SuspiciousMethodCalls")
-        int index = children.indexOf(node);
-        if (index != -1) {
-          toRemove.add(node);
-          minIndex = Math.min(minIndex, index);
-        }
+    List<XDebuggerTreeNode> toRemove = new ArrayList<>();
+    for (XDebuggerTreeNode node : nodes) {
+      @SuppressWarnings("SuspiciousMethodCalls")
+      int index = children.indexOf(node);
+      if (index != -1) {
+        toRemove.add(node);
+        minIndex = Math.min(minIndex, index);
       }
     }
     myRootNode.removeChildren(toRemove);
 
     List<? extends WatchNode> newChildren = myRootNode.getWatchChildren();
-    if (newChildren != null && !newChildren.isEmpty()) {
-      WatchNode node = minIndex < newChildren.size() ? newChildren.get(minIndex) : newChildren.get(newChildren.size() - 1);
+    if (!newChildren.isEmpty()) {
+      WatchNode node = newChildren.get(Math.min(minIndex, newChildren.size() - 1));
       TreeUtil.selectNode(getTree(), node);
     }
     updateSessionData();
diff --git a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTree.java b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTree.java
index bfdb5a7b45f8..08360d67d2aa 100644
--- a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTree.java
+++ b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTree.java
@@ -364,12 +364,7 @@ public class XDebuggerTree extends DnDAwareTree implements DataProvider, Disposa
 
   private static void markNodesObsolete(final XValueContainerNode<?> node) {
     node.setObsolete();
-    List<? extends XValueContainerNode<?>> loadedChildren = node.getLoadedChildren();
-    if (loadedChildren != null) {
-      for (XValueContainerNode<?> child : loadedChildren) {
-        markNodesObsolete(child);
-      }
-    }
+    node.getLoadedChildren().forEach(XDebuggerTree::markNodesObsolete);
   }
 
   @Nullable
diff --git a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTreeRestorer.java b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTreeRestorer.java
index 1796deaa41be..c041f186c012 100644
--- a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTreeRestorer.java
+++ b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTreeRestorer.java
@@ -36,8 +36,8 @@ import java.util.Map;
 public class XDebuggerTreeRestorer implements XDebuggerTreeListener, TreeSelectionListener {
   private final XDebuggerTree myTree;
   private final Rectangle myLastVisibleNodeRect;
-  private final Map<XDebuggerTreeNode, XDebuggerTreeState.NodeInfo> myNode2State = new HashMap<XDebuggerTreeNode, XDebuggerTreeState.NodeInfo>();
-  private final Map<RestorableStateNode, XDebuggerTreeState.NodeInfo> myNode2ParentState = new HashMap<RestorableStateNode, XDebuggerTreeState.NodeInfo>();
+  private final Map<XDebuggerTreeNode, XDebuggerTreeState.NodeInfo> myNode2State = new HashMap<>();
+  private final Map<RestorableStateNode, XDebuggerTreeState.NodeInfo> myNode2ParentState = new HashMap<>();
   private boolean myStopRestoringSelection;
   private boolean myInsideRestoring;
 
@@ -51,12 +51,7 @@ public class XDebuggerTreeRestorer implements XDebuggerTreeListener, TreeSelecti
   private void restoreChildren(final XDebuggerTreeNode treeNode, final XDebuggerTreeState.NodeInfo nodeInfo) {
     if (nodeInfo.isExpanded()) {
       myTree.expandPath(treeNode.getPath());
-      List<? extends XDebuggerTreeNode> children = treeNode.getLoadedChildren();
-      if (children != null) {
-        for (XDebuggerTreeNode child : children) {
-          restoreNode(child, nodeInfo);
-        }
-      }
+      treeNode.getLoadedChildren().forEach(child -> restoreNode(child, nodeInfo));
       myNode2State.put(treeNode, nodeInfo);
     }
   }
diff --git a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTreeState.java b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTreeState.java
index 4a1c1f154570..e83b624744a9 100644
--- a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTreeState.java
+++ b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/XDebuggerTreeState.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2015 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -61,24 +61,22 @@ public class XDebuggerTreeState {
   private void addChildren(final XDebuggerTree tree, final NodeInfo nodeInfo, final XDebuggerTreeNode treeNode) {
     if (tree.isExpanded(treeNode.getPath())) {
       List<? extends XDebuggerTreeNode> children = treeNode.getLoadedChildren();
-      if (children != null) {
-        nodeInfo.myExpanded = true;
-        for (XDebuggerTreeNode child : children) {
-          final TreePath path = child.getPath();
-          final Rectangle bounds = tree.getPathBounds(path);
-          if (bounds != null) {
-            Rectangle treeVisibleRect =
-              tree.getParent() instanceof JViewport ? ((JViewport)tree.getParent()).getViewRect() : tree.getVisibleRect();
-            if (treeVisibleRect.contains(bounds)) {
-              myLastVisibleNodeRect = bounds;
-            }
-          }
-          NodeInfo childInfo = createNode(child, tree.isPathSelected(path));
-          if (childInfo != null) {
-            nodeInfo.addChild(childInfo);
-            addChildren(tree, childInfo, child);
+      nodeInfo.myExpanded = true;
+      for (XDebuggerTreeNode child : children) {
+        TreePath path = child.getPath();
+        Rectangle bounds = tree.getPathBounds(path);
+        if (bounds != null) {
+          Rectangle treeVisibleRect =
+            tree.getParent() instanceof JViewport ? ((JViewport)tree.getParent()).getViewRect() : tree.getVisibleRect();
+          if (treeVisibleRect.contains(bounds)) {
+            myLastVisibleNodeRect = bounds;
           }
         }
+        NodeInfo childInfo = createNode(child, tree.isPathSelected(path));
+        if (childInfo != null) {
+          nodeInfo.addChild(childInfo);
+          addChildren(tree, childInfo, child);
+        }
       }
     }
   }
diff --git a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/MessageTreeNode.java b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/MessageTreeNode.java
index 3197ad8b6417..4763046910e3 100644
--- a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/MessageTreeNode.java
+++ b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/MessageTreeNode.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2009 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -84,9 +84,10 @@ public class MessageTreeNode extends XDebuggerTreeNode {
     return myLink;
   }
 
+  @NotNull
   @Override
   public List<? extends XDebuggerTreeNode> getLoadedChildren() {
-    return null;
+    return Collections.emptyList();
   }
 
   @Override
diff --git a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/WatchesRootNode.java b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/WatchesRootNode.java
index 4c70dacda133..7fc574dd6567 100644
--- a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/WatchesRootNode.java
+++ b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/WatchesRootNode.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2015 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,7 +18,6 @@ package com.intellij.xdebugger.impl.ui.tree.nodes;
 import com.intellij.icons.AllIcons;
 import com.intellij.openapi.util.registry.Registry;
 import com.intellij.util.ArrayUtil;
-import com.intellij.util.ObjectUtils;
 import com.intellij.util.containers.ContainerUtil;
 import com.intellij.util.ui.tree.TreeUtil;
 import com.intellij.xdebugger.Obsolescent;
@@ -91,11 +90,10 @@ public class WatchesRootNode extends XValueContainerNode<XValueContainer> {
     }
   }
 
-  @Nullable
+  @NotNull
   @Override
   public List<? extends XValueContainerNode<?>> getLoadedChildren() {
-    List<? extends XValueContainerNode<?>> empty = Collections.<XValueGroupNodeImpl>emptyList();
-    return ContainerUtil.concat(myChildren, ObjectUtils.notNull(super.getLoadedChildren(), empty));
+    return ContainerUtil.concat(myChildren, super.getLoadedChildren());
   }
 
   @NotNull
@@ -232,33 +230,24 @@ public class WatchesRootNode extends XValueContainerNode<XValueContainer> {
 
     @Override
     public void evaluated(@NotNull final XValue result) {
-      DebuggerUIUtil.invokeLater(new Runnable() {
-        @Override
-        public void run() {
-          WatchesRootNode root = (WatchesRootNode)myResultPlace.getParent();
-          root.replaceNode(myResultPlace, new WatchNodeImpl(root.myTree, root, result, myResultPlace.getExpression()));
-        }
+      DebuggerUIUtil.invokeLater(() -> {
+        WatchesRootNode root = (WatchesRootNode)myResultPlace.getParent();
+        root.replaceNode(myResultPlace, new WatchNodeImpl(root.myTree, root, result, myResultPlace.getExpression()));
       });
     }
 
     @Override
     public void errorOccurred(@NotNull final String errorMessage) {
-      DebuggerUIUtil.invokeLater(new Runnable() {
-        @Override
-        public void run() {
-          WatchesRootNode root = (WatchesRootNode)myResultPlace.getParent();
-          root.replaceNode(myResultPlace, createErrorNode(root.myTree, root, myResultPlace.getExpression(), errorMessage));
-        }
+      DebuggerUIUtil.invokeLater(() -> {
+        WatchesRootNode root = (WatchesRootNode)myResultPlace.getParent();
+        root.replaceNode(myResultPlace, createErrorNode(root.myTree, root, myResultPlace.getExpression(), errorMessage));
       });
     }
 
     public void noSession() {
-      DebuggerUIUtil.invokeLater(new Runnable() {
-        @Override
-        public void run() {
-          WatchesRootNode root = (WatchesRootNode)myResultPlace.getParent();
-          root.replaceNode(myResultPlace, createMessageNode(root.myTree, root, myResultPlace.getExpression()));
-        }
+      DebuggerUIUtil.invokeLater(() -> {
+        WatchesRootNode root = (WatchesRootNode)myResultPlace.getParent();
+        root.replaceNode(myResultPlace, createMessageNode(root.myTree, root, myResultPlace.getExpression()));
       });
     }
   }
diff --git a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/XDebuggerTreeNode.java b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/XDebuggerTreeNode.java
index 5e3101bff21a..64e9e1aab706 100644
--- a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/XDebuggerTreeNode.java
+++ b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/XDebuggerTreeNode.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2009 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -175,7 +175,7 @@ public abstract class XDebuggerTreeNode implements TreeNode, TreeSpeedSearch.Pat
     return myPath;
   }
 
-  @Nullable
+  @NotNull
   public abstract List<? extends XDebuggerTreeNode> getLoadedChildren();
 
   public abstract void clearChildren();
diff --git a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/XValueContainerNode.java b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/XValueContainerNode.java
index 2148fb4c2b3a..7538e676065b 100644
--- a/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/XValueContainerNode.java
+++ b/platform/xdebugger-impl/src/com/intellij/xdebugger/impl/ui/tree/nodes/XValueContainerNode.java
@@ -234,7 +234,7 @@ public abstract class XValueContainerNode<ValueContainer extends XValueContainer
   }
 
   @Override
-  @Nullable
+  @NotNull
   public List<? extends XValueContainerNode<?>> getLoadedChildren() {
     List<? extends XValueContainerNode<?>> empty = Collections.<XValueGroupNodeImpl>emptyList();
     return ContainerUtil.concat(ObjectUtils.notNull(myTopGroups, empty),