Bug 203044 Invoke Script does not work correctly for two similar charts [13]
chart/org.eclipse.birt.chart.device.extension/src/org/eclipse/birt/chart/device/image/JavaxImageIOWriter.java
super.after( );
		if ( _oOutputIdentifier != null )
		{
			
			Iterator it = null;
			String s = getFormat( );
			if ( s != null )
			{
				it = ImageIO.getImageWritersByFormatName( s );
				if ( !it.hasNext( ) )
				{
					it = null; 
				}
			}
			
			if ( it == null )
			{
				s = getMimeType( );
				if ( s == null )
				{
					throw new ChartException( ChartDeviceExtensionPlugin.ID,
							ChartException.RENDERING,
							"JavaxImageIOWriter.exception.no.imagewriter.mimetype.and.format",
							new Object[]{
									getMimeType( ),
									getFormat( ),
									getClass( ).getName( )
							},
							Messages.getResourceBundle( getULocale( ) ) );
				}