code: private CompressedISPNChangesBuffer getChangesBufferSafe()
     {
        CompressedISPNChangesBuffer changesContainer = changesList.get();
        if (changesContainer == null)
        {
           throw new IllegalStateException("changesContainer should not be empty");
        }
        return changesContainer;
     }
docs: Tries to get buffer and if it is null throws an exception otherwise returns buffer.
  
  @return