NullReferenceException on close of query after removing a subquery (4251362)

When removing a subquery from a query and then closing it, the following exception error message is displayed:

"System.NullReferenceException
Object reference not set to an instance of an object.
Stack Trace:
   at bh.a(DockManager A_0, XmlTextWriter A_1, Boolean A_2)
   at ActiproSoftware.UIStudio.Dock.DockManager.SaveToolWindowLayoutToFile(String path, Boolean saveTextProperties)
   at Quest.Toad.QueryBuilder.QueryBuilderControl.SaveDockLayout()
   at Quest.Toad.QueryBuilder.QueryBuilderControl.Dispose(Boolean disposing)
   at System.ComponentModel.Component.Dispose()
   at Quest.Toad.QueryBuilder.QueryBuilder.Dispose(Boolean disposing)
   at System.ComponentModel.Component.Dispose()
   at System.Windows.Forms.Control.Dispose(Boolean disposing)
   at System.Windows.Forms.ContainerControl.Dispose(Boolean disposing)
   at ActiproSoftware.WinUICore.UIContainerControl.Dispose(Boolean disposing)
   at ActiproSoftware.UIStudio.Dock.DocumentWindow.Dispose(Boolean disposing)
   at System.ComponentModel.Component.Dispose()
   at ActiproSoftware.UIStudio.Dock.DockManager.a(TabbedMdiWindow[] A_0, Boolean A_1, TabbedMdiWindowCloseReason A_2)
   at ActiproSoftware.UIStudio.Dock.DocumentWindow.Close(TabbedMdiWindowCloseReason reason)
   at ActiproSoftware.UIStudio.Dock.TabbedMdiWindow.Close()
   at Quest.Toad.Gui.MainForm.CloseDocument(DocumentForm document)
   at Quest.Toad.Gui.MainForm.closeButton_ItemClick(Object sender, ItemClickEventArgs e)
   at DevExpress.XtraBars.BarItem.OnClick(BarItemLink link)
   at DevExpress.XtraBars.BarBaseButtonItem.OnClick(BarItemLink link)
   at DevExpress.XtraBars.BarItemLink.OnLinkClick()
   at DevExpress.XtraBars.BarItemLink.OnLinkAction(BarLinkAction action, Object actionArgs)
   at DevExpress.XtraBars.BarButtonItemLink.OnLinkAction(BarLinkAction action, Object actio