presto-main/src/main/java/io/prestosql/util/JsonUtil.java/RowBlockBuilderAppender/append
class RowBlockBuilderAppender:        @Override
        public void append(JsonParser parser, BlockBuilder blockBuilder)
                throws IOException
        {
            if (parser.getCurrentToken() == JsonToken.VALUE_NULL) {
                blockBuilder.appendNull();
                return;
            }

            if (parser.getCurrentToken() != START_ARRAY && parser.getCurrentToken() != START_OBJECT) {
                throw new JsonCastException(format("Expected a json array or object, but got %s", parser.getText()));
            }

            parseJsonToSingleRowBlock(
                    parser,
                    (SingleRowBlockWriter) blockBuilder.beginBlockEntry(),
                    fieldAppenders,
                    fieldNameToIndex);
            blockBuilder.closeEntry();
        }