private static @Nullable String getAdjacentSide(final String side, final String toEdge, final String fromEdge) {
    if (side.equals(toEdge)) {
      return null;
    }
    if (side.equals(fromEdge)) {
      return BorderLayout.CENTER;
    }
    return toEdge;
  }
private static @Nullable String getAdjacentSide(final String side, final String toEdge, final String fromEdge)