code: @Nullable
    public synchronized List<ProducerContextCallbacks> setIsPrefetchNoCallbacks(boolean isPrefetch) {
      if (isPrefetch == mIsPrefetch) {
        return null;
      }
      mIsPrefetch = isPrefetch;
      return new ArrayList<>(mCallbacks);
    }
docs: Changes isPrefetch property.
  
  <p> This method does not call any callbacks. Instead, caller of this method is responsible for
  iterating over returned list and calling appropriate method on each callback object.
  {@see #callOnIsPrefetchChanged}
  
  @return list of callbacks if the value actually changes, null otherwise