jstedfast/MailKit · error · ArgumentNullException

buffer

Error message

buffer

What it means

Guard in HMACMD5.ComputeHash: the 'buffer' argument (the input data to hash) was null. The hash computation needs a real byte array, so null is rejected with ArgumentNullException before range checks on offset/count.

Solutions

1. Allocate or fetch the buffer before hashing
2. Use ComputeHash(emptyArray) if hashing an empty payload intentionally
3. Catch ArgumentNullException at the signing boundary

Example fix

// before
hmac.ComputeHash(payload, 0, payload.Length);
// after
if (payload != null)
	hmac.ComputeHash(payload, 0, payload.Length);

if (buffer == null) throw new ArgumentException("buffer must not be null");

bool HasData(byte[] b) => b != null;

try { hmac.ComputeHash(buf, off, cnt); } catch (ArgumentNullException) { /* null payload */ }

When it happens

Trigger: Calling ComputeHash(null, 0, 0), often when the message body came from an upstream null value.

Common situations: NTLM signing of a message whose payload buffer was never populated.

Related errors

• value
• ArgumentNullException
• ArgumentNullException
• ArgumentNullException
• ArgumentNullException

AI-assisted analysis of jstedfast/MailKit@9d3859a785 (2026-09-15). Data as JSON: /api/errors/08ab35827c957443. Report an issue: GitHub.

Appendix: source

Thrown at MailKit/Security/Ntlm/HMACMD5.cs:103

			hash.Reset ();

			return value;
		}

		public void Initialize ()
		{
			hash.Init (new KeyParameter (Key));
		}

		public void Clear ()
		{
			Dispose (false);
		}

		public byte[] ComputeHash (byte[] buffer, int offset, int count)
		{
			if (buffer == null)
				throw new ArgumentNullException (nameof (buffer));

			if (offset < 0 || offset > buffer.Length)
				throw new ArgumentOutOfRangeException (nameof (offset));

			if (count < 0 || offset > buffer.Length - count)
				throw new ArgumentOutOfRangeException (nameof (count));

			if (disposed)
				throw new ObjectDisposedException ("HashAlgorithm");

			HashCore (buffer, offset, count);
			hashValue = HashFinal ();

			return hashValue;
		}

		public byte[] ComputeHash (byte[] buffer)
		{

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