Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/SelectionChoiceHandle.java
{
	/**
	 * Constructs the handle of selection choice.
	 * 
	 * @param valueHandle
	 *            the value handle for selection choice list of one property
	 * @param index
	 *            the position of this selection choice in the list
	 */
	public SelectionChoiceHandle( SimpleValueHandle valueHandle, int index )
	{
		super( valueHandle, index );