presto-main/src/main/java/io/prestosql/server/SliceSerialization.java/SliceDeserializer/deserialize
class SliceDeserializer:        @Override
        public Slice deserialize(JsonParser jsonParser, DeserializationContext deserializationContext)
                throws IOException
        {
            return utf8Slice(jsonParser.readValueAs(String.class));
        }