Code can't handle @ in user_id

In my organization, we use the work emails to configure the user_id property.
As of now, your code can't handle @ in the user_id as it gets ValidationException.
Here is my workaround:
var user_id_components = user_id_arn.split("/");
var user_id = user_id_components[user_id_components.length-1].split('@')[0];
returned_event_fields["user_id"] = user_id;