Bug 198917 set __parameterpage to false for required parameter will cause wrong Exception[0705]
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/EngineTask.java
*            the value for the parameter
	 * @return true if the given parameter value is valid; false otherwise
	 */
	private boolean validateScalarParameter( ScalarParameterHandle paramHandle )
			throws ParameterValidationException
	{
		String paramName = paramHandle.getName( );
		Object paramValue = runValues.get( paramName );
		String type = paramHandle.getDataType( );
		
		if ( paramValue == null )
		{
			if ( !paramHandle.isRequired( ) )
				return true;
			log.log( Level.SEVERE, "Parameter {0} doesn't allow a null value.",  
					paramName );
			
			throw new ParameterValidationException(
					MessageConstants.NULL_PARAMETER_EXCEPTION,
					new String[]{paramName} );
		}
		String source = paramHandle.getValidate( );
		if ( source != null && source.length( ) != 0 )
		{
			Object result = executionContext.evaluate( source );
			if ( !( result instanceof Boolean )
					|| !( (Boolean) result ).booleanValue( ) )
			{
				log.log( Level.SEVERE, "Parameter validate failed: ",  
						source );