code: public void removeChangeListener(@NonNull ListenerToken token) {
          if (token == null) { throw new IllegalArgumentException("token cannot be null."); }
  
          synchronized (lock) {
              mustBeOpen();
              if (token instanceof ChangeListenerToken && ((ChangeListenerToken) token).getKey() != null) {
                  removeDocumentChangeListener((ChangeListenerToken) token);
              }
              else { removeDatabaseChangeListener(token); }
          }
      }
docs: Remove the given DatabaseChangeListener from the this database.
  
  @param token