base: Ensure room name is not empty

Ruma used to handle this during deserialization when the field was
an Option.

Especially meaningful when computing the room name, where
an empty string means the name is not set.

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

crates/matrix-sdk-base/src/rooms/normal.rs

@@ -350,6 +350,8 @@ impl Room {
     }
 
     /// Get the `m.room.name` of this room.
+    ///
+    /// The returned string is guaranteed not to be empty.
     pub fn name(&self) -> Option<String> {
         self.inner.read().name().map(ToOwned::to_owned)
     }
@@ -1022,7 +1024,8 @@ impl RoomInfo {
     }
 
     fn name(&self) -> Option<&str> {
-        Some(&self.base_info.name.as_ref()?.as_original()?.content.name)
+        let name = &self.base_info.name.as_ref()?.as_original()?.content.name;
+        (!name.is_empty()).then_some(name)
     }
 
     fn tombstone(&self) -> Option<&RoomTombstoneEventContent> {
@@ -1356,6 +1359,19 @@ mod tests {
         assert_eq!(room.display_name().await.unwrap(), DisplayName::Empty);
     }
 
+    #[async_test]
+    async fn display_name_for_invited_room_is_empty_if_room_name_empty() {
+        let (_, room) = make_room(RoomState::Invited);
+
+        let room_name = MinimalStateEvent::Original(OriginalMinimalStateEvent {
+            content: RoomNameEventContent::new(String::new()),
+            event_id: None,
+        });
+        room.inner.update(|info| info.base_info.name = Some(room_name));
+
+        assert_eq!(room.display_name().await.unwrap(), DisplayName::Empty);
+    }
+
     #[async_test]
     async fn display_name_for_invited_room_uses_canonical_alias_if_available() {
         let (_, room) = make_room(RoomState::Invited);