std::optional<std::chrono::year_month_day> to DATE error if optional is empty about libpqxx

[tt4g]

I think this is a bug because libpqxx has to send NULL to the database when std::optional<T> is std::nullopt.
However, the actual error message is "0001-00-00 BC", so I don't know where this date string came from.

Maybe the datestyle is different from what libpqxx assumes, as described in the hint "Perhaps you need a different "datestyle" setting.".
What style is set for datestyle?

[jtv]

@Alfrink it's important when reporting a bug to whittle it down to the minimal stand-alone reproduction. In other words, the absolute simplest but complete code that showcases the problem.

I tried reproducing the problem like this:

  pqxx::connection conn;
  pqxx::transaction tx{conn};
  tx.exec0("CREATE TEMP TABLE pqxx_dates (i integer, d date)");
  auto const null_date{std::optional<std::chrono::year_month_day>{}};
  tx.exec_params0(
    "INSERT INTO pqxx_dates(i, d) VALUES ($1, $2)", 1, null_date);
  auto const r{tx.exec1("SELECT d FROM pqxx_dates")};
  assert(r[0].is_null());

However, this code succeeded.

It looks to me more like what you're passing is not an empty optional, but something more like a zero of some kind.