presto-main/src/main/java/io/prestosql/block/BlockJsonSerde.java/BlockJsonSerde/deserialize
class BlockJsonSerde:        @Override
        public Block deserialize(JsonParser jsonParser, DeserializationContext deserializationContext)
                throws IOException
        {
            byte[] decoded = Base64.getDecoder().decode(jsonParser.readValueAs(String.class));
            return readBlock(blockEncodingSerde, Slices.wrappedBuffer(decoded));
        }