@Override
    public Object convert(Inspector value) {
        if ( ! value.valid()) return null;
        if (value.type() == Type.STRING) return value.asString();
        return new FeatureData(value);
    }
Class representing a "feature data" field: A map of values which are
either floats or tensors.
container-search/src/main/java/com/yahoo/prelude/fastsearch/FeatureDataField.java