Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/SortKeyHandle.java
/*******************************************************************************
 * Copyright (c) 2004 Actuate Corporation.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *  Actuate Corporation  - initial API and implementation
 *******************************************************************************/
package org.eclipse.birt.report.model.api;
import org.eclipse.birt.report.model.api.activity.SemanticException;
import org.eclipse.birt.report.model.api.elements.structures.SortKey;
/**
 * Represents the handle of sort key structure. The sort key is the sort entry
 * for a table or list item, it defines the column and sort direction pair. Each
 * sort key has the following properties:
 * 
 * <p>
 * <dl>
 * <dt><strong>Column Name </strong></dt>
 * <dd>the name of the column that is sorted.</dd>
 * 
 * <dt><strong>Direction </strong></dt>
 * <dd>the sort direction:asc or desc.</dd>
 * </dl>
 *  
 */
public class SortKeyHandle extends StructureHandle