Using net6.0.
Using CsvHelper 30.0.1

So when building locally the build succeeds without issue, however when committing to Github the Build fails with the following error:

CsvHelper.TypeConversion.TypeConverterException : The conversion cannot be performed.
    Text: '03/20/2023'
    MemberName: StartDate
    MemberType: System.Nullable`1[[System.DateTime, System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]]
    TypeConverter: 'CsvHelper.TypeConversion.NullableConverter'
IReader state:
   ColumnCount: 0
   CurrentIndex: 2
   HeaderRecord:
["Id","Name","StartDate","TotalSpend"]
IParser state:
   ByteCount: 0
   CharCount: 56
   Row: 2
   RawRow: 2
   Count: 4
   RawRecord:
1,Test name,03/20/2023,0.12

Here is the code:
`

public class CsvProcessingServiceTests
 {
    public void GetCsvStreamAsTransactionTypeTest()
    {
        var testObject = new CsvProcessingServiceTestObject
        {
            Id = 1,
            Name = "Test name",
            StartDate = DateTime.ParseExact("2023-03-20", "yyyy-MM-dd", 
                       CultureInfo.GetCultureInfo("en-GB")),
            TotalSpend = (decimal?)0.12
        };
        var testObjectInput = testObject.GetCSV();
        var testStream = new MemoryStream(Encoding.UTF8.GetBytes(testObjectInput));

        var result = _csvProcessingService.GetCsvStreamAsTransactionType<CsvProcessingServiceTestObject>(new StreamReader(testStream));
    }

    private class CsvProcessingServiceTestObject
    {
        public string GetCSV()
        {
            var objectAsString = new StringBuilder();
            objectAsString.Append("Id,Name,StartDate,TotalSpend\n");
            objectAsString.Append($"{Id},{Name},{StartDate?.Date.ToString("d")},{TotalSpend}");
    
            return objectAsString.ToString();
        }
    
        public int? Id { get; set; }
        public string? Name { get; set; }
        public DateOnly? StartDate { get; set; }
        public decimal? TotalSpend { get; set; }
    }
}

public class CsvProcessingService {
    private readonly CsvConfiguration _csvConfiguration;
    public CsvProcessingService()
    {
        _csvConfiguration = new CsvConfiguration(CultureInfo.GetCultureInfo("en-GB"))
        {
            TrimOptions = TrimOptions.Trim,
            HeaderValidated = null,
            MissingFieldFound = null
        };
    }

    public List<T> GetCsvStreamAsTransactionType<T>(StreamReader inputStreamReader)
    {
        using var sr = new StreamReader(inputStreamReader);
        using var csv = new CsvReader(sr, _csvConfiguration);
        var csvRecords = csv.GetRecords<T>().ToList();
        return csvRecords;
    }
}

`

Anyone have any ideas? I changed the (StartDate) DateTime to DateOnly but that also seemed to fail. It only seems to work when StartDate is set to a string.
Is there an issue with the GitHub Build? Why does it work when running locally in VS but not when commited to GitHub?

>Solution :

Try changing your GetCsv to provide culture info for StartDate?.Date.ToString:

objectAsString.Append($"{Id},{Name},{StartDate?.Date.ToString("d", CultureInfo.GetCultureInfo("en-GB"))},{TotalSpend}");

en-Gb should process dates as day–month–year while 03/20/2023 (value from error) obviously is not.

Or just use fixed custom formatting and do not rely on culture and standard formats.