Bug 193886 NPE is thrown when preview external CSS style in ppt[1205]
engine/org.eclipse.birt.report.engine.emitter.ppt/src/org/eclipse/birt/report/engine/emitter/ppt/PPTRender.java
}
	public void visitContainer( IContainerArea container )
	{
		startContainer( container );
		Iterator iter = container.getChildren( );
		while ( iter.hasNext( ) )
		{
			IArea child = (IArea) iter.next( );
			child.accept( this );
		}
		endContainer( container );
	}
	/**
	 * If the container is a PageArea, this method creates a new page. If the
	 * container is the other containerAreas, such as TableArea, or just the
	 * border of textArea/imageArea this method draws the border and background