Bug 207250 Check blank value for datetime type parameter from url.[0002][0705]
Description: Check blank value for datetime type parameter from url. Build number:2.3.0.v20071023 Steps to reproduce: 1. New a datetime parameter mydt,listbox, tick off isRequired. 2. Preview in external browser and add "&dt=" in url, press enter. Expected result: Error message to indicate blank value isn't allowed for this parameter. Actual result: No error message and blank value is accepted. I tried to new a jsp and use <birt:paramDef> to pass the blank value and the blank value is accepted,too. Error log:n/a
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/context/ViewerAttributeBean.java
* 
	 * @param request
	 * @return
	 */
	protected long getLastModifiedOfDesign( HttpServletRequest request )
	{
		String designFile = ParameterAccessor.getParameter( request,
				ParameterAccessor.PARAM_REPORT );
		if ( designFile == null )
			return -1L;
		
		File file = new File( this.reportDesignName );
		if ( file != null && file.exists( ) )
		{
			if ( file.isFile( ) )
				return file.lastModified( );
		}
		else
		{
			
			try
			{
				if ( !designFile.startsWith( "/" ) ) 
					designFile = "/" + designFile; 
				URL url = request.getSession( ).getServletContext( )
						.getResource( designFile );
				if ( url != null )
					return url.openConnection( ).getLastModified( );
			}
			catch ( Exception e )