Bug 153523 OK button in parameter dialog is enabled without default value in combo-box
Description: OK button in parameter dialog is enabled without default value in combo-box Steps to reproduce: 1. New a report parameter, combo-box. 2. Click New button, input abc as value, click OK 3. Set abc as default value and close Edit Parameter dialog. 4. New a data source and dataset 5. Edit the parameter, remove abc value and import values from dataset Expected result: OK button is disabled for there is no default value. Actual result: OK button is enabled.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/CascadingParametersDialog.java
value = getColumnName( parameter, COLUMN_VALUE );
				}
				else if ( COLUMN_DISPLAY_TEXT.equals( property ) )
				{
					value = getColumnName( parameter, COLUMN_DISPLAY_TEXT );
				}
				if ( value == null )
				{
					value = ""; 
				}
				return value;
			}
			return ""; 
		}
		public void modify( Object element, String property, Object value )
		{
			Object actualElement = ( (TableItem) element ).getData( );
			try
			{
				saveParameterProperties( );
			}
			catch ( SemanticException e1 )
			{
				e1.printStackTrace( );
			}
			if ( COLUMN_NAME.equals( property ) )
			{
				try
				{
					if ( actualElement == newParameter )