Bug 145274 __isnull does not work properly when parameters have default value
steps to reproduce: - create a report - add a parameter with default value - preview report in web viewer - modify the url with __null pattern expected behavior: - __null takes effect actual behavior: - it simply didn't
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/context/ViewerAttributeBean.java
* Get report service instance.
	 */
	protected IViewerReportService getReportService( )
	{
		return BirtReportServiceFactory.getReportService( );
	}
	/**
	 * Clear our resources.
	 * 
	 * @exception Throwable
	 * @return
	 */
	protected void __finalize( ) throws Throwable
	{
	}
	/**
	 * get parsed parameters.
	 * 
	 * @param design
	 *            IViewerReportDesignHandle
	 * @param parameterList
	 *            Collection
	 * @param request
	 *            HttpServletRequest
	 * @param options
	 *            InputOptions
	 * 
	 * @return Map
	 */
	protected Map getParsedParameters( IViewerReportDesignHandle design,