NullReferenceException when authenticating using SaslMechanismNtlm

[StefanBertels]

ImapClient.Authenticate(mechanism: new SaslMechanismNtlm(NetworkCredential)) throws NullReferenceException with latest MailKit

• Windows Server 2019
• .NET 5.0
• MailKit 2.10.1
• Server is Microsoft Exchange

Downgrading to Version 2.9.0 solves my issue for now (without changing anything else).
Authentication is done via user+password against Microsoft Exchange.

System.NullReferenceException: Object reference not set to an instance of an object.
   at byte[] MailKit.Security.Ntlm.Type3Message.Encode() in D:/src/MailKit/MailKit/Security/Ntlm/Type3Message.cs:line 270
   at byte[] MailKit.Security.SaslMechanismNtlm.Challenge(byte[] token, int startIndex, int length) in D:/src/MailKit/MailKit/Security/SaslMechanismNtlm.cs:line 218
   at string MailKit.Security.SaslMechanism.Challenge(string token) in D:/src/MailKit/MailKit/Security/SaslMechanism.cs:line 290
   at async Task MailKit.Net.Imap.ImapClient.AuthenticateAsync(SaslMechanism mechanism, bool doAsync, CancellationToken cancellationToken)+(?) => { } in D:/src/MailKit/MailKit/Net/Imap/ImapClient.cs:line 833
   at async Task<bool> MailKit.Net.Imap.ImapCommand.StepAsync(bool doAsync) in D:/src/MailKit/MailKit/Net/Imap/ImapCommand.cs:line 854
   at async Task MailKit.Net.Imap.ImapEngine.IterateAsync(bool doAsync) in D:/src/MailKit/MailKit/Net/Imap/ImapEngine.cs:line 2108
   at async Task MailKit.Net.Imap.ImapEngine.RunAsync(ImapCommand ic, bool doAsync) in D:/src/MailKit/MailKit/Net/Imap/ImapEngine.cs:line 2158
   at async Task MailKit.Net.Imap.ImapClient.AuthenticateAsync(SaslMechanism mechanism, bool doAsync, CancellationToken cancellationToken) in D:/src/MailKit/MailKit/Net/Imap/ImapClient.cs:line 845
   at void MailKit.Net.Imap.ImapClient.Authenticate(SaslMechanism mechanism, CancellationToken cancellationToken) in D:/src/MailKit/MailKit/Net/Imap/ImapClient.cs:line 913