The application_id field on the channel object is now documented as nullable, and will be serialized as null in some cases.
The application_id field on the channel object is now nullable. For future guild channels, this field can be serialized as null. For group DMs, there are no plans to serialize this field as null.
Because the field was not previously documented as nullable, this is a slightly breaking change. If your app or library assumes application_id is always a snowflake when present, you'll need to update it to handle null. The field continues to be optional.