let render_webxdc_status_update_object() return an Option; add a test for that

src/mimefactory.rs

@@ -1163,10 +1163,10 @@ impl<'a> MimeFactory<'a> {
             let json = self.msg.param.get(Param::Arg).unwrap_or_default();
             parts.push(context.build_status_update_part(json).await);
         } else if self.msg.viewtype == Viewtype::Webxdc {
-            let json = context
+            if let Some(json) = context
                 .render_webxdc_status_update_object(self.msg.id, None)
-                .await?;
+                .await?
-            if json != r#"{{"updates":[]}}"# {
+            {
                 parts.push(context.build_status_update_part(&json).await);
             }
         }

src/webxdc.rs

@@ -157,7 +157,8 @@ impl Context {
                         instance_msg_id,
                         Some(status_update_id),
                     )
-                    .await?,
+                    .await?
+                    .ok_or_else(|| format_err!("Status object expected."))?,
                 );
                 status_update.set_quote(self, Some(&instance)).await?;
                 let status_update_msg_id =
@@ -257,11 +258,15 @@ impl Context {
         &self,
         instance_msg_id: MsgId,
         status_update_id: Option<StatusUpdateId>,
-    ) -> Result<String> {
+    ) -> Result<Option<String>> {
         let updates_array = self
             .get_webxdc_status_updates(instance_msg_id, status_update_id)
             .await?;
-        Ok(format!(r#"{{"updates":{}}}"#, updates_array))
+        if updates_array == "[]" {
+            Ok(None)
+        } else {
+            Ok(Some(format!(r#"{{"updates":{}}}"#, updates_array)))
+        }
     }
 }
 
@@ -717,6 +722,31 @@ mod tests {
         Ok(())
     }
 
+    #[async_std::test]
+    async fn test_render_webxdc_status_update_object() -> Result<()> {
+        let t = TestContext::new_alice().await;
+        let chat_id = create_group_chat(&t, ProtectionStatus::Unprotected, "a chat").await?;
+        let mut instance = create_webxdc_instance(
+            &t,
+            "minimal.xdc",
+            include_bytes!("../test-data/webxdc/minimal.xdc"),
+        )
+        .await?;
+        chat_id.set_draft(&t, Some(&mut instance)).await?;
+        assert!(t
+            .render_webxdc_status_update_object(instance.id, None)
+            .await?
+            .is_none());
+
+        t.send_webxdc_status_update(instance.id, "1", "bla").await?;
+        assert!(t
+            .render_webxdc_status_update_object(instance.id, None)
+            .await?
+            .is_some());
+
+        Ok(())
+    }
+
     #[async_std::test]
     async fn test_draft_and_send_webxdc_status_update() -> Result<()> {
         let alice = TestContext::new_alice().await;