Make the announce info field optional

crates/librqbit/src/create_torrent_file.rs

@@ -200,7 +200,7 @@ pub async fn create_torrent<'a>(
     let info_hash = compute_info_hash(&info).context("error computing info hash")?;
     Ok(CreateTorrentResult {
         meta: TorrentMetaV1Owned {
-            announce: b""[..].into(),
+            announce: None,
             announce_list: Vec::new(),
             info,
             comment: None,

crates/librqbit/src/session.rs

@@ -721,10 +721,7 @@ impl Session {
                 .map(|t| ByteString(t.into_bytes()))
                 .collect();
             let info = TorrentMetaV1Owned {
-                announce: trackers
-                    .first()
-                    .cloned()
-                    .unwrap_or_else(|| ByteString(b"http://retracker.local/announce".to_vec())),
+                announce: trackers.first().cloned(),
                 announce_list: vec![trackers],
                 info: storrent.info,
                 comment: None,