fix(hydra): Don't serialise null room IDs in PDUs

Cargo.toml

@@ -387,6 +387,7 @@ features = [
     "unstable-msc4210", # remove legacy mentions
     "unstable-extensible-events",
     "unstable-pdu",
+	"unstable-msc4155"
 ]
 
 [workspace.dependencies.rust-rocksdb]

src/core/matrix/pdu.rs

@@ -31,6 +31,7 @@ use crate::Result;
 pub struct Pdu {
 	pub event_id: OwnedEventId,
 
+	#[serde(skip_serializing_if = "Option::is_none")]
 	pub room_id: Option<OwnedRoomId>,
 
 	pub sender: OwnedUserId,

src/service/rooms/timeline/backfill.rs

@@ -7,7 +7,6 @@ use conduwuit_core::{
 		event::Event,
 		pdu::{PduCount, PduId, RawPduId},
 	},
-	trace,
 	utils::{IterStream, ReadyExt},
 	validated, warn,
 };