Bug 136270 Group's data binding column can only be used by the group itself
If you add some data binding columns to a group, these columns can only be used by this group itself. It should has a way to make the child can use the parent group's data binding column.
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DEUtil.java
public static String resolveNull( String value )
	{
		return value == null ? "" : value; 
	}
	/**
	 * Converts the RGB object value to a String, the String format is "r,g,b",
	 * no quotation marks.
	 * 
	 * @param rgb
	 *            RGB value.
	 * @return String value.
	 */
	public static String getRGBText( RGB rgb )
	{
		if ( rgb != null )
		{
			return rgb.red + "," + rgb.green + "," + rgb.blue; 
		}
		return ""; 
	}
	/**
	 * Converts the String value to an RGB object value, the String format is
	 * "r,g,b", no quotation marks.
	 * 
	 * @param val
	 *            String value.
	 * @return RGB value.
	 */
	public static RGB getRGBValue( String val )
	{