Bug 190727 [regression]Default value issue when switch report parameter from textbox to listbox.[0705]
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
.findChoice( DesignChoiceConstants.STRING_FORMAT_TYPE_UNFORMATTED )
					.getDisplayName( );
			previewString = "True"; 
		}
		else
		{
			displayFormat = choiceSet.findChoice( formatCategroy )
					.getDisplayName( );
			if ( isCustom( ) )
			{
				displayFormat += ": " + formatPattern; 
			}
			if ( defaultValue != null )
			{
				previewString = format( defaultValue );
			}
			else
			{
				if ( type.equals( DesignChoiceConstants.PARAM_TYPE_DATETIME ) )
				{
					previewString = new DateFormatter( isCustom( ) ? formatPattern
							: ( formatCategroy.equals( DesignChoiceConstants.DATETIEM_FORMAT_TYPE_UNFORMATTED ) ? DateFormatter.DATETIME_UNFORMATTED
									: formatCategroy ),
							ULocale.getDefault( ) ).format( new Date( ) );
				}
				else if ( type.equals( DesignChoiceConstants.PARAM_TYPE_DATE ) )
				{
					previewString = new DateFormatter( isCustom( ) ? formatPattern
							: ( formatCategroy.equals( DesignChoiceConstants.DATE_FORMAT_TYPE_UNFORMATTED ) ? DateFormatter.DATE_UNFORMATTED
									: formatCategroy ),