[Storage] Fix NullReferenceException when parsing error response (Azure#48268)

Author: jalauzon-msft

sdk/storage/Azure.Storage.Common/CHANGELOG.md

@@ -7,6 +7,7 @@
 ### Breaking Changes
 
 ### Bugs Fixed
+- Fixed bug where in rare cases, a `NullReferenceException` could be thrown when parsing an error response from the service.
 
 ### Other Changes
 

sdk/storage/Azure.Storage.Common/src/Shared/Constants.cs

@@ -105,7 +105,9 @@ internal static class Constants
         public const string TrueName = "true";
 
         public const string ErrorCode = "Code";
+        public const string ErrorCodeLower = "code";
         public const string ErrorMessage = "Message";
+        public const string ErrorMessageLower = "message";
 
         public const string CommaString = ",";
         public const char CommaChar = ',';

sdk/storage/Azure.Storage.Common/src/Shared/StorageRequestFailedDetailsParser.cs

@@ -27,10 +27,12 @@ public override bool TryParse(Response response, out ResponseError? error, out I
                     if (response.Headers.ContentType.Contains(Constants.ContentTypeApplicationXml))
                     {
                         XDocument xml = XDocument.Load(contentStream);
-                        var errorCode = xml.Root!.Element(Constants.ErrorCode)!.Value;
-                        var message = xml.Root.Element(Constants.ErrorMessage)!.Value;
-                        data = new Dictionary<string, string>();
+                        var errorCode = xml.Root!.Element(Constants.ErrorCode)?.Value ??
+                            xml.Root.Element(Constants.ErrorCodeLower)?.Value;
+                        var message = xml.Root.Element(Constants.ErrorMessage)?.Value ??
+                            xml.Root.Element(Constants.ErrorMessageLower)?.Value;
 
+                        data = new Dictionary<string, string>();
                         foreach (XElement element in xml.Root.Elements())
                         {
                             switch (element.Name.LocalName)