Bug 153038 NPE when delete master page content in old report design.
UI/org.eclipse.birt.report.designer.ui.editors.schematic/src/org/eclipse/birt/report/designer/internal/ui/editors/layout/ReportEditorWithPalette.java
if ( getModel( ) != null )
		{
			getGraphicalViewer( ).setContents( getModel( ) );
			hookModelEventManager( getModel());
		}
		viewer.addDropTargetListener( createTemplateTransferDropTargetListener( viewer ) );
	}
	
	protected void hookModelEventManager(Object model)
	{	
		manager.hookRoot( model);
		Object processor = getGraphicalViewer( ).getRootEditPart( ).getAdapter(IModelEventProcessor.class);
		if (processor instanceof IModelEventProcessor)
		{
			manager.addModelEventProcessor( (IModelEventProcessor)processor );
		}
		if (getCommandStack( ) instanceof WrapperCommandStack)
		{
			manager.hookCommandStack( (WrapperCommandStack)getCommandStack( ) );
		}
	}
	
	protected void unhookModelEventManager(Object model)
	{	
		manager.unhookRoot( model);
		if (getCommandStack( ) instanceof WrapperCommandStack)
		{
			manager.unhookCommandStack( (WrapperCommandStack)getCommandStack( ) );
		}
	}