assertThrows(NullPointerException.class, () -> J.join(ITERABLE_NULL.iterator()));
    assertThrows(NullPointerException.class, () -> J.join(ITERABLE_1_NULL_2.iterator()));
  }

  public void testOnCharOverride() {
    Joiner onChar = Joiner.on('-');
    checkNoOutput(onChar, ITERABLE_);
    checkResult(onChar, ITERABLE_1, "1");
    checkResult(onChar, ITERABLE_12, "1-2");
    checkResult(onChar, ITERABLE_123, "1-2-3");