public String asString() {
        if (string == null) {
            string = Utf8Codec.decode(value, 0, value.length);
        }
        return string;
    }
A value type encapsulating a String in its UTF-8 representation.
Useful for lazy decoding; if the data is just passed through in
UTF-8 it will never be converted at all.

@author havardpe
vespajlib/src/main/java/com/yahoo/slime/Utf8Value.java