291 (#318)

* #291 change throw error to return null

* add jsDoc

* fix room null error

example/gist-bot/on-friend.ts

@@ -30,6 +30,7 @@ export async function onFriend(contact: Contact, request?: FriendRequest): Promi
 
     if (request.hello === 'ding') {
       const myRoom = await Room.find({ topic: 'ding' })
+      if (!myRoom) return
       setTimeout(function() {
         myRoom.add(contact)
         myRoom.say('welcome ' + contact.name())

example/gist-bot/on-message.ts

@@ -36,6 +36,7 @@ export async function onMessage(message: Message): Promise<void> {
       message.say('thanks for ding me')
 
       const myRoom = await Room.find({ topic: 'ding' })
+      if (!myRoom) return
 
       if (myRoom.has(sender)) {
         sender.say('no need to ding again, because you are already in ding room')