Fix a rare error regarding interactions

#9218

src/rest/RequestHandler.js

@@ -40,7 +40,7 @@ const captchaMessage = [
 ];
 
 function parseResponse(res) {
-  if (res.headers.get('content-type').startsWith('application/json')) return res.json();
+  if (res.headers.get('content-type')?.startsWith('application/json')) return res.json();
   return res.arrayBuffer(); // Cre: TheDevYellowy
 }