didSelectMessage:converstation: called with no message

When an user receives a message with the extension opened, didSelectMessage:converstation: is called with nil as the first parameter. The documentation about this method states that this method "Informs the extension that a new message has been selected in the conversation." and the first parameter, message is "The message selected". It never states that this message might be nullable or this method is triggered while receiving a message.

I've filled a radar #28191502 but I'm not sure if it's either a bug or a misunderstanding from the documentation.