SDK sending empty message even though message object is initialized

[BobAmmerman]

I have an application that uses the GraphAPI SDK version 6.70 to send emails. On occasion I have seen a 400 error claiming that there were no valid recipients in the email. This is reinforced by the fact that logging the raw HTTP request shows an empty message. However, I am logging the contents of the Message object before and after sending, and in both cases it is properly initialized including a TO recipient, subject and body. Retrying using the same message object fails again with another 400. However, if I create a new message object and send that it usually succeeds. Any ideas?

[Kurt Geminic (kgeminicdev)]

The cause is the SDK's backing store. Graph models only serialize properties marked as changed. After any serialization through the SDK's serializers, all properties are marked clean (InitializationCompleted = true). So serializing the same Message instance a second time gives {} and you get a 400 for "no recipients". That's why your retry with the same object fails and a fresh object works.

It also explains the occasional first-attempt failure, if anything serialized the object before the send. A common culprit is logging it with KiotaJsonSerializer. The Graph client enables the backing store on the default serializer registry too, so that call also marks everything clean.

Fixes:

// before re-sending an object that was already serialized
message.BackingStore.InitializationCompleted = false; // marks all properties dirty again
await graphClient.Users[userId].SendMail.PostAsync(body);

For logging, ask for the full object so the dirty flags are left alone:

var json = await KiotaJsonSerializer.SerializeAsStringAsync(message, serializeOnlyChangedValues: false);

Building a new Message for each attempt also avoids the problem.