public static void serializeStringField(JsonGenerator generator, FieldBase field, StringFieldValue value) {
        // Hide fields which only contains an empty string
        if (value.getString().length() == 0 && field != null) {
            return;
        }
        serializeString(generator, field, value.getString());
    }
@author Steinar Knutsen
@author Vegard Sjonfjell
document/src/main/java/com/yahoo/document/json/JsonSerializationHelper.java