docs: @SuppressWarnings("unchecked")
      public MergeObservableList<T> insertList(@NonNull ObservableList<? extends T> list) {
          list.addOnListChangedCallback(callback);
          int oldSize = size();
          lists.add(list);
          modCount += 1;
          if (!list.isEmpty()) {
              listeners.notifyInserted(this, oldSize, list.size());
          }
          return this;
      }