presto-main/src/main/java/io/prestosql/server/ExpressionSerialization.java/ExpressionSerialization/serialize
class ExpressionSerialization:        @Override
        public void serialize(Expression expression, JsonGenerator jsonGenerator, SerializerProvider serializerProvider)
                throws IOException
        {
            jsonGenerator.writeString(ExpressionFormatter.formatExpression(expression));
        }