groupPolicy property
GroupPolicy decides every inbound GROUP or THREAD message — a thread is a group surface — defaulting to "open". "open" admits every sender in the room. "allowlist" admits only what Group lists, so an EMPTY Group blocks the channel's group rooms outright. "disabled" drops all of them.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
String? groupPolicy;