jstedfast/MailKit · error · ArgumentNullException

data

Error message

data

What it means

MailKit's WinRT-based KeyedHashAlgorithm wrapper (used for CRAM-MD5/NTLM on UWP) throws ArgumentNullException with parameter name "data" when ComputeHash is called with a null buffer. The buffer must be a real byte array because it is converted into an IBuffer via CryptographicBuffer.CreateFromByteArray before hashing.

Solutions

1. Ensure the input byte array is non-null before calling ComputeHash (e.g., use ?? Array.Empty<byte>() if empty input is legal for your protocol).
2. Check that the code producing the buffer (stream read, challenge decode) succeeded and did not return null.
3. Note this is a null check, not a disposed-check — if you also see ObjectDisposedException, check disposal separately.

Example fix

// before
byte[] hmac = hasher.ComputeHash(challengeBytes); // challengeBytes may be null

// after
byte[] hmac = hasher.ComputeHash(challengeBytes ?? Array.Empty<byte>());

if (buffer == null) throw new InvalidOperationException("challenge bytes missing");
byte[] hash = hasher.ComputeHash(buffer);

static bool HasData(byte[] b) => b != null && b.Length > 0;

try {
    var hash = hasher.ComputeHash(buffer);
} catch (ArgumentNullException) {
    // null input: regenerate the buffer or abort the auth exchange
}

When it happens

Trigger: Calling ComputeHash((byte[]) null) on a disposed-or-valid keyed hash context — the null check fires before any use of the underlying hmac object.

Common situations: Hashing data read from a stream or SASL challenge where the byte-array conversion step returned null; passing an uninitialized field; a custom SASL mechanism that passes the raw (null) challenge through.

Related errors

• ArgumentNullException
• contentType
• inputBuffer
• InvalidChallenge
• outputBuffer

AI-assisted analysis of jstedfast/MailKit@9d3859a785 (2026-09-15). Data as JSON: /api/errors/99eb7b53771fbd9a. Report an issue: GitHub.

Appendix: source

Thrown at MailKit/Security/KeyedHashAlgorithm.cs:75

		/// <summary>
		/// Computes the hash code for the buffer.
		/// </summary>
		/// <remarks>
		/// Computes the hash code for the buffer.
		/// </remarks>
		/// <returns>The computed hash code.</returns>
		/// <param name="buffer">The buffer.</param>
		/// <exception cref="System.ArgumentNullException">
		/// <paramref name="buffer"/> is <c>null</c>.
		/// </exception>
		/// <exception cref="System.ObjectDisposedException">
		/// The keyed hash algorithm context has been disposed.
		/// </exception>
		public byte[] ComputeHash (byte[] buffer)
		{
			if (buffer == null)
				throw new ArgumentNullException ("data");

			hmac.Append (CryptographicBuffer.CreateFromByteArray (buffer));
			var value = hmac.GetValueAndReset ();
			byte[] hash;

			CryptographicBuffer.CopyToByteArray (value, out hash);

			return hash;
		}

		/// <summary>
		/// Releases all resource used by the <see cref="MailKit.Security.KeyedHashAlgorithm"/> object.
		/// </summary>
		/// <remarks>Call <see cref="Dispose()"/> when you are finished using the <see cref="MailKit.Security.KeyedHashAlgorithm"/>. The
		/// <see cref="Dispose()"/> method leaves the <see cref="MailKit.Security.KeyedHashAlgorithm"/> in an unusable state. After calling
		/// <see cref="Dispose()"/>, you must release all references to the <see cref="MailKit.Security.KeyedHashAlgorithm"/> so the
		/// garbage collector can reclaim the memory that the <see cref="MailKit.Security.KeyedHashAlgorithm"/> was occupying.</remarks>
		public void Dispose ()

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