public String convert(ILoggingEvent le) {
    List<Marker> markers = le.getMarkers();
    if (markers == null || markers.isEmpty()) {
      return EMPTY;
    } else {
      return markers.toString();
    }
  }
@Test
  public void testWithNullMarker() {
    String result = converter.convert(createLoggingEvent(null));
    assertEquals("[null]", result);
  }