Bug 175664 [Mac] Unexpected internal exception occurs when invoke expression builder
Description: There are two problems: 1. "fx" button (Click this button to invoke Expression Builder) could not be displayed correctly, nothing displayed in the button. 2. Click on the button, an unexpected internal exception occurs. Version:2.2.0.v20070205 Steps to reproduce: 1.Insert a Data item to the layout. Click "fx" button to invoke the expression builder, although on Mac "fx" button could not display correctly. Error log: Argument cannot be null Plug-in Provider: Eclipse.org Plug-in Name: BIRT Designer UI Plug-in ID: org.eclipse.birt.report.designer.ui Error Code: Error.GUIException.invokedByUnexpectedException Error Message:Argument cannot be null
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/internal/ui/util/UIUtil.java
{
		Point compositeSize = composite.getSize( );
		GC gc = new GC( composite );
		Image image = new Image( Display.getCurrent( ),
				compositeSize.x,
				compositeSize.y );
		gc.copyArea( image, 0, 0 );
		gc.dispose( );
		return image;
	}
	public static ModelEventManager getModelEventManager( )
	{
		IEditorPart input = null;
		String ids[] = {
				"org.eclipse.birt.report.designer.ui.editors.ReportEditor",
				"org.eclipse.birt.report.designer.ui.editors.LibraryEditor",
				"org.eclipse.birt.report.designer.ui.editors.TemplateEditor"
		};
		
		for(int i = 0; i < ids.length; i ++)
		{
			input = getActiveEditor( ids[i] );
			if(input != null)
			{
				break;
			}
		}			
		
		if ( input == null )
			return null;