NullReferenceException in CertificateUtil

[ChrWeinert]

The call
dotnet run -- createcertchain -s "My CA" -p mypassword -i 3
results in the following Runtime error:

Unhandled Exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object.
at RW.DPSCertificateTool.CertificateUtil.CreateCaCertificate(String subjectName, String certificatePassword, X509Certificate2 issuingCa) in C:\source\local\AzureIoTDPSCertificates-master\AzureIoTDPSCertificates-master\src\DPSCertificateTool\CertificateUtil.cs:line 73
at RW.DPSCertificateTool.CreateCertChain.OnExecute() in C:\source\local\AzureIoTDPSCertificates-master\AzureIoTDPSCertificates-master\src\DPSCertificateTool\CreateCertChain.cs:

[ChrWeinert]

I found the Problem and solution within the CreateCaCertificate-Method of the CertificateUtil-Class:

if (issuingCa != null)
{
// set the AuthorityKeyIdentifier. There is no built-in
// support, so it needs to be copied from the Subject Key
// Identifier of the signing certificate and massaged slightly.
// AuthorityKeyIdentifier is "KeyID="
// var issuerSubjectKey = issuingCa.Extensions["Subject Key Identifier"].RawData;
byte[] issuerSubjectKey = null;
foreach (var item in issuingCa.Extensions)
{
if(item.Oid.Value == "2.5.29.14")
{
issuerSubjectKey = item.RawData;
break;
}
}

               var segment = new ArraySegment<byte>(issuerSubjectKey, 2, issuerSubjectKey.Length - 2);
                var authorityKeyIdentifier = new byte[segment.Count + 4];
                // these bytes define the "KeyID" part of the AuthorityKeyIdentifer
                authorityKeyIdentifier[0] = 0x30;
                authorityKeyIdentifier[1] = 0x16;
                authorityKeyIdentifier[2] = 0x80;
                authorityKeyIdentifier[3] = 0x14;
                segment.CopyTo(authorityKeyIdentifier, 4);
                request.CertificateExtensions.Add(new X509Extension("2.5.29.35", authorityKeyIdentifier, false));
            } [Configuration.CA].RawData;

[rwatjen]

Sorry for the late response, I've been offline on vacation.

I am unable to reproduce the problem. The extension with OID 2.5.29.14 is "Subject Key Identifier" (as you already knew).
I don't know why that shouldn't have a name on your computer, or has it perhaps been localized?

What are the properties of the 2.5.29.14 extension on your computer, specifically the item.Oid.FriendlyName ?