Bug 119550 Default Value of Named Expression can't be saved in design file
New a report, set named expression in the report property editor add a named expression and set the default value add a report item, say table, to the layout set the named expression of the report item add a named expression and set hte default value save the report close the report and reopen, and there is no default named expression value displayed. open report design file with a text editor, there is no default value associate with the named expression
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/core/UserPropertyDefn.java
* @param choiceArray
	 *            choice array to be set.
	 */
	public void setChoices( UserChoice[] choiceArray )
	{
		if ( choiceArray == null )
		{
			details = null;
			return;
		}
		
		ChoiceSet choices = new ChoiceSet( null );
		choices.setChoices( choiceArray );
		details = choices;
	}
	/**
	 * Checks whether <code>displayName</code> matches any items in the choice
	 * set for an extended choice property type on a user defined choice set. If
	 * <code>displayName</code> exists in the choice set, return the name of
	 * this choice. Otherwise, return <code>null</code>.
	 * 
	 * @param module
	 *            the module
	 * @param displayName
	 *            the candidate display name
	 * @return the choice name if found. Otherwise, return <code>null</code>.
	 */
	protected String validateExtendedChoicesByDisplayName( Module module,
			String displayName )
	{