docs: public Registration removeRegistration(String topic, String id) {
          Registration registration = registrationIdMap.remove(id);
          if (registration != null) {
              final Collection<Registration> all = registrations.get(topic);
              if (all != null) {
                  all.remove(registration);
              }
              pingNotifiableEventListener(topic, registration, false);
          }
          return registration;
      }