[FIX] If InternalHubot_Username is undefined then rocket.cat should be default bot (#16371)

app/ui/client/lib/chatMessages.js

@@ -424,7 +424,7 @@ export class ChatMessages {
 						ts: new Date(),
 						msg: TAPi18n.__('No_such_command', { command: s.escapeHTML(match[1]) }),
 						u: {
-							username: settings.get('InternalHubot_Username'),
+							username: settings.get('InternalHubot_Username') || 'rocket.cat',
 						},
 						private: true,
 					};