private Inspector valueAt(int index) {
            if (dataValues[index] != null) {
                return new Value.DataValue(dataValues[index]);
            }
            return new Value.DoubleValue(doubleValues[index]);
        }
MatchFeatureData helps pack match features for hits into
inspectable HitValue objects, all sharing the same Hashlet
for the field names.

@author arnej
vespajlib/src/main/java/com/yahoo/data/access/helpers/MatchFeatureData.java