From d06a1d698cbc75ce11af423d6a4a618d8742f618 Mon Sep 17 00:00:00 2001
From: "David R. Williamson" <drwill@microsoft.com>
Date: Mon, 12 Jul 2021 15:33:42 -0700
Subject: [PATCH] Document ArgumentNull

---
 iothub/service/src/Common/Exceptions/ErrorCode.cs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/iothub/service/src/Common/Exceptions/ErrorCode.cs b/iothub/service/src/Common/Exceptions/ErrorCode.cs
index 838e8c3bf7..5c16184b65 100644
--- a/iothub/service/src/Common/Exceptions/ErrorCode.cs
+++ b/iothub/service/src/Common/Exceptions/ErrorCode.cs
@@ -50,7 +50,12 @@ public enum ErrorCode
         // Note: one example found in logs is for invalid characters in a twin property name.
         ArgumentInvalid = 400004,
 
+        /// <summary>
+        /// Something in the payload is unexpectedly null. Check the error message for more information about what is invalid.
+        /// </summary>
+        // Note: an example suggested is null method payloads, but our client converts null to a JSON null, which is allowed.
         ArgumentNull = 400005,
+
         IotHubFormatError = 400006,
 
         /// <summary>