[no bug] Outline could have been closed/dismissed.
diff --git a/bundles/org.eclipse.wst.xsd.ui/src-adt/org/eclipse/wst/xsd/ui/internal/adt/outline/ADTContentOutlineProvider.java b/bundles/org.eclipse.wst.xsd.ui/src-adt/org/eclipse/wst/xsd/ui/internal/adt/outline/ADTContentOutlineProvider.java
index 7f8697f..f46967d 100644
--- a/bundles/org.eclipse.wst.xsd.ui/src-adt/org/eclipse/wst/xsd/ui/internal/adt/outline/ADTContentOutlineProvider.java
+++ b/bundles/org.eclipse.wst.xsd.ui/src-adt/org/eclipse/wst/xsd/ui/internal/adt/outline/ADTContentOutlineProvider.java
@@ -109,8 +109,11 @@
     if (viewer instanceof TreeViewer)
     {
       TreeViewer treeViewer = (TreeViewer) viewer;
-      treeViewer.refresh(object);
-      treeViewer.reveal(object);
+      if (treeViewer.getTree() != null && !treeViewer.getTree().isDisposed())
+      {
+        treeViewer.refresh(object);
+        treeViewer.reveal(object);
+      }
     }
   }