assertThrows(NullPointerException.class, () -> J.join(iterableNull.iterator()));
    assertThrows(NullPointerException.class, () -> J.join(iterable1Null2.iterator()));
  }

  public void testOnCharOverride() {
    Joiner onChar = Joiner.on('-');
    checkNoOutput(onChar, iterable);
    checkResult(onChar, iterable1, "1");
    checkResult(onChar, iterable12, "1-2");
    checkResult(onChar, iterable123, "1-2-3");