allow selecting conference option

lib/microsoft_graph.rb

@@ -17,11 +17,21 @@ class MicrosoftGraph
   end
 
   def create_teams_meeting(subject)
+    if @refresh_token.nil? || @token_expires_at.nil?
+      raise ActionController::InvalidAuthenticityToken, 'Missing refresh token / token expiration'
+      return
+    end
+
     # Obtain new token if token is expired or will expire in less than 5 minutes
     if 5.minutes.from_now.to_i > @token_expires_at.seconds
       refresh_access_token
     end
 
+    if @token.nil?
+      raise ActionController::InvalidAuthenticityToken, 'Missing access token'
+      return
+    end
+
     response = HTTParty.post(
       "#{BASE_URL}/me/onlineMeetings",
       body: {