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src/DotNetOpenAuth/Messaging/Reflection/IMessagePartEncoder.cs

@@ -7,6 +7,7 @@
 namespace DotNetOpenAuth.Messaging.Reflection {
 	using System;
 	using System.Collections.Generic;
+	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using System.Text;
 
@@ -16,6 +17,7 @@ namespace DotNetOpenAuth.Messaging.Reflection {
 	/// <remarks>
 	/// Implementations of this interface must include a default constructor and must be thread-safe.
 	/// </remarks>
+	[ContractClass(typeof(IMessagePartEncoderContract))]
 	public interface IMessagePartEncoder {
 		/// <summary>
 		/// Encodes the specified value.
@@ -32,4 +34,45 @@ public interface IMessagePartEncoder {
 		/// <exception cref="FormatException">Thrown when the string value given cannot be decoded into the required object type.</exception>
 		object Decode(string value);
 	}
+
+	/// <summary>
+	/// Code contract for the <see cref="IMessagePartEncoder"/> type.
+	/// </summary>
+	[ContractClassFor(typeof(IMessagePartEncoder))]
+	internal abstract class IMessagePartEncoderContract : IMessagePartEncoder {
+		/// <summary>
+		/// Initializes a new instance of the <see cref="IMessagePartEncoderContract"/> class.
+		/// </summary>
+		protected IMessagePartEncoderContract() {
+		}
+
+		#region IMessagePartEncoder Members
+
+		/// <summary>
+		/// Encodes the specified value.
+		/// </summary>
+		/// <param name="value">The value.  Guaranteed to never be null.</param>
+		/// <returns>
+		/// The <paramref name="value"/> in string form, ready for message transport.
+		/// </returns>
+		string IMessagePartEncoder.Encode(object value) {
+			Contract.Requires<ArgumentNullException>(value != null);
+			throw new NotImplementedException();
+		}
+
+		/// <summary>
+		/// Decodes the specified value.
+		/// </summary>
+		/// <param name="value">The string value carried by the transport.  Guaranteed to never be null, although it may be empty.</param>
+		/// <returns>
+		/// The deserialized form of the given string.
+		/// </returns>
+		/// <exception cref="FormatException">Thrown when the string value given cannot be decoded into the required object type.</exception>
+		object IMessagePartEncoder.Decode(string value) {
+			Contract.Requires<ArgumentNullException>(value != null);
+			throw new NotImplementedException();
+		}
+
+		#endregion
+	}
 }

src/DotNetOpenAuth/Messaging/Reflection/MessageDescriptionCollection.cs

@@ -78,7 +78,6 @@ internal class MessageDescriptionCollection {
 		[Pure]
 		internal MessageDictionary GetAccessor(IMessage message) {
 			Contract.Requires<ArgumentNullException>(message != null);
-			ErrorUtilities.VerifyArgumentNotNull(message, "message");
 			return this.Get(message).GetDictionary(message);
 		}