Merge pull request #12025 from dotnet/main

Merge main into live

Author: dotnet-policy-service[bot]

xml/System.Net.Http/MultipartContent.xml

@@ -52,7 +52,10 @@
   </Attributes>
   <Docs>
     <summary>Provides a collection of <see cref="T:System.Net.Http.HttpContent" /> objects that get serialized using the multipart/* content type specification.</summary>
-    <remarks>To be added.</remarks>
+    <remarks>
+Multipart messages must contain one or more body parts. When a <see cref="T:System.Net.Http.MultipartContent" /> instance with zero parts is serialized, it's written as a single empty part with no content headers or message body.
+If your server doesn't support such contents with zero parts, consider conditionally using a different <see cref="T:System.Net.Http.HttpContent" /> type or no <see cref="T:System.Net.Http.HttpContent" />.
+    </remarks>
   </Docs>
   <Members>
     <MemberGroup MemberName=".ctor">