* @return the Column that was requested if it exists.
* @throws NotFoundException if the result doesn't exist (including if the value holds a tumbstone)
*/
public static IColumn validateAndGetColumn(List<Row> rows, ByteBuffer columnName) throws NotFoundException {
if(rows.isEmpty())
throw new NotFoundException();
if(rows.size() > 1)
throw new RuntimeException("Block id returned more than one row");
Row row = rows.get(0);
if(row.cf == null)
throw new NotFoundException();
IColumn col = row.cf.getColumn(columnName);
if(col == null || !col.isLive())
throw new NotFoundException();
return col;
}