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
{
	/**
	 * Viewer preview max rows limited
	 */
	private int maxRows;
	/**
	 * Report parameters as string map
	 */
	private Map parametersAsString = null;
	/**
	 * Constructor.
	 * 
	 * @param request
	 */
	public ViewerAttributeBean( HttpServletRequest request )
	{
		try
		{
			init( request );
		}
		catch ( Exception e )