Bug 182673 No default value error message prompts incorrectly
Steps to reproduce: 1. New a report parameter; 2. Choose control type as Combo; 3. Choose parameter as dynamic type; Expected result: As the isRequired is false by default, parameter's default value can be null value. There should be no error message about no default value prompt. Actual result; Error messages prompts
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/CascadingParametersDialog.java
private List getColumnList()
	{
		List columnList = new ArrayList();
		DataSetHandle dataSetHandle = getDataSet( selectedParameter );
		try
		{
			columnList = DataUtil.getColumnList( dataSetHandle );
		}
		catch ( SemanticException e )
		{
			ExceptionHandler.handle( e );
		}
		return ( columnList.isEmpty( ) )? Collections.EMPTY_LIST : columnList;
	}
	
	private List getColumnValueList( )
	{
		ArrayList valueList = new ArrayList( );
		DataEngine engine;
		DataSetHandle dataSet = getDataSet( selectedParameter );
		try
		{
			String queryExpr = null;
			engine = DataEngine.newDataEngine( DataEngineContext.newInstance( DataEngineContext.DIRECT_PRESENTATION,
					null,
					null,
					null ) );
			BaseQueryDefinition query = (BaseQueryDefinition) DataUtil.getPreparedQuery( engine,
					dataSet )
					.getReportQueryDefn( );