BinaryExporter exception when read char values

[SoftStoneDevelop]

Steps to reproduce

            using (var connection = new NpgsqlConnection(root.GetConnectionString("SqlConnection")))
            {
                connection.Open();
                var cmd = connection.CreateCommand();
                cmd.CommandText = @"
CREATE TABLE IF NOT EXISTS public.charTable
(
    id serial NOT NULL,
    value char NOT NULL,
    CONSTRAINT charTable_pkey PRIMARY KEY (id)
);
";
                cmd.ExecuteNonQuery();

                cmd.CommandText = @"
INSERT INTO public.charTable
(value)
VALUES
($1)
";
                var parametr = new NpgsqlParameter<char>();
                parametr.NpgsqlValue = 'd';
                cmd.Parameters.Add(parametr);
                cmd.ExecuteNonQuery();

                parametr.NpgsqlValue = 's';
                cmd.ExecuteNonQuery();

                using (var export = connection.BeginBinaryExport(@"

COPY public.charTable
(
    id,
    value
) TO STDOUT (FORMAT BINARY)

"))
                {
                    while (export.StartRow() != -1)
                    {
                        var id = export.Read<int>();//got NullReferenceException on second iteration
                        var value = export.Read<char>();
                    }
                }
            }

The issue

First iteration is works fine, but when i excpect on the second iteration where value must be 's' I get throw Exception(some times nullreference, some times Npgsql.NpgsqlException : Unknown message code: 100 seems 100 is 'd')

Exception message:
Stack trace:
System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=Npgsql
  StackTrace:
   at Npgsql.NpgsqlBinaryExporter.<DoRead>d__29`1.MoveNext()
   at System.Threading.Tasks.ValueTask`1.get_Result()
   at System.Runtime.CompilerServices.ValueTaskAwaiter`1.GetResult()
   at Npgsql.NpgsqlBinaryExporter.Read[T]()
   at NpgsqlBenchmark.Tests.CharExportTest.Test() in E:\Work\SoftStoneDevelop github\NpgsqlBinaryExporter\Src\NpgsqlBenchmark\Tests\CharExportTest.cs:line 57

  This exception was originally thrown at this call stack:
    [External Code]
    NpgsqlBenchmark.Tests.CharExportTest.Test() in CharExportTest.cs

Further technical details

Npgsql version: 7.0.4
PostgreSQL version: PostgreSQL 15.2, compiled by Visual C++ build 1914, 64-bit
Operating system:
Edition Windows 10 Pro
Version 22H2
OS build 19045.3086

[SoftStoneDevelop]

Repository with test code: https://github.com/SoftStoneDevelop/NpgsqlBinaryExporter

[vonzshik]

Hello. Yep, I can confirm there is indeed a bug with how we read char values. Thank you for raising this issue!