code: @Nonnull
    public EChange removeObject (@Nullable final CALLBACKTYPE aCallback)
    {
      if (aCallback == null)
        return EChange.UNCHANGED;
  
      return m_aRWLock.writeLocked ( () -> m_aCallbacks.removeObject (aCallback));
    }
docs: Remove the specified callback
  
  @param aCallback
  May be <code>null</code>.
  @return {@link EChange}