Bug 120503 Cascading Parameter can not drop into layout
Details: Cascading Parameter can not drop into layout Step: 1.Open a report design and Create a Sample Data Source and data set by "select * from CLASSICMODELS.CUSTOMERS" 2.New a cascading parameter and create CUSTOMERSNUMBER and CUSTOMERSNAME in parameter named number and name. Press OK 3.Drop parameter name into layout. Actual results: The parameter in Cascading Parameter Group can not drop to layout
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DEUtil.java
}
	/**
	 * Gets the proper expression for the given model
	 * 
	 * @param model
	 *            the given model
	 * @return Returns the proper expression for the given model, or null if no
	 *         proper one exists
	 */
	public static String getExpression( Object model )
	{
		if ( model instanceof ParameterHandle )
		{
			return IReportElementConstants.PARAMETER_PREFIX
					+ "[\"" + escape( ( (ParameterHandle) model ).getQualifiedName( ) ) + "\"]"; 
		}
		if ( model instanceof DataSetItemModel )
		{
			String colName = ( (DataSetItemModel) model ).getAlias( );
			if ( colName == null || colName.trim( ).length( ) == 0 )
			{
				colName = ( (DataSetItemModel) model ).getName( );
			}
			return getColumnExpression( colName );
		}
		return null;
	}
	/**
	 * Returns the integer font size for string value.
	 *