Throw exception with helpful message if duplicate webhook config values exists.

Octokit/Exceptions/RepositoryWebHookConfigException.cs

@@ -0,0 +1,60 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Globalization;
+using System.Linq;
+using System.Runtime.Serialization;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Octokit
+{
+#if !NETFX_CORE
+    [Serializable]
+#endif
+    [SuppressMessage("Microsoft.Design", "CA1032:ImplementStandardExceptionConstructors",
+        Justification = "These exceptions are specific to the GitHub API and not general purpose exceptions")]
+    public class RepositoryWebHookConfigException : Exception
+    {
+        readonly string message;
+
+        public RepositoryWebHookConfigException(IEnumerable<string> invalidConfig)
+        {
+            var parameterList = string.Join(", ", invalidConfig.Select(ic => ic.FromRubyCase()));
+            message = string.Format(CultureInfo.InvariantCulture,
+                "Duplicate webhook config values found - these values: {0} should not be passed in as part of the config values. Use the properties on the NewRepositoryWebHook class instead.",
+                parameterList);
+        }
+
+        public override string Message
+        {
+            get { return message; }
+        }
+
+#if !NETFX_CORE
+        /// <summary>
+        /// Constructs an instance of RepositoryWebHookConfigException
+        /// </summary>
+        /// <param name="info">
+        /// The <see cref="SerializationInfo"/> that holds the
+        /// serialized object data about the exception being thrown.
+        /// </param>
+        /// <param name="context">
+        /// The <see cref="StreamingContext"/> that contains
+        /// contextual information about the source or destination.
+        /// </param>
+        protected RepositoryWebHookConfigException(SerializationInfo info, StreamingContext context)
+            : base(info, context)
+        {
+            if (info == null) return;
+            message = info.GetString("Message");
+        }
+
+        public override void GetObjectData(SerializationInfo info, StreamingContext context)
+        {
+            base.GetObjectData(info, context);
+            info.AddValue("Message", Message);
+        }
+#endif
+    }
+}