code: public void addAddOnInstallationStatusListener(AddOnInstallationStatusListener listener) {
          if (listener == null) {
              throw new IllegalArgumentException("Parameter listener must not be null.");
          }
  
          if (addOnInstallationStatusListeners == null) {
              addOnInstallationStatusListeners = new ArrayList<>();
          }
          addOnInstallationStatusListeners.add(listener);
      }
docs: Adds the given {@code listener} to the extension hook, to be later notified of changes in the installation status of the
  add-ons.
  
  @param listener the listener that will be added and then notified
  @throws IllegalArgumentException if the given {@code listener} is {@code null}.
  @since 2.5.0