function accumulateInto(current, next) {
  !(next != null) ? process.env.NODE_ENV !== 'production' ? invariant(false, 'accumulateInto(...): Accumulated items must not be null or undefined.') : _prodInvariant('30') : void 0;

  if (current == null) {
    return next;
  }

  // Both are not empty. Warning: Never call x.concat(y) when you are not
  // certain that x is an Array (x could be a string with concat method).
  if (Array.isArray(current)) {
    if (Array.isArray(next)) {
      current.push.apply(current, next);
      return current;
    }
    current.push(next);
    return current;
  }

  if (Array.isArray(next)) {
    // A bit too dangerous to mutate `next`.
    return [current].concat(next);
  }

  return [current, next];
}
Enqueues a callback to be invoked when `notifyAll` is invoked.

@param {function} callback Invoked when `notifyAll` is invoked.
@param {?object} context Context to call `callback` with.
@internal