Collection<@Nullable String> c = MinimalCollection.of("a", null, "b");
    assertThrows(
        NullPointerException.class, () -> ImmutableMultiset.copyOf((Collection<String>) c));
  }

  public void testCopyOf_multiset_empty() {
    Multiset<String> c = HashMultiset.create();
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertTrue(multiset.isEmpty());
  }

  public void testCopyOf_multiset_oneElement() {

    Collection<@Nullable String> c = MinimalCollection.of("a", null, "b");
    assertThrows(
        NullPointerException.class, () -> ImmutableMultiset.copyOf((Collection<String>) c));
  }

  public void testCopyOf_multiset_empty() {
    Multiset<String> c = HashMultiset.create();
    Multiset<String> multiset = ImmutableMultiset.copyOf(c);
    assertTrue(multiset.isEmpty());
  }

  public void testCopyOf_multiset_oneElement() {

    Collection<String> c = MinimalCollection.of("a", null, "b");
    assertThrows(NullPointerException.class, () -> ImmutableSortedMultiset.copyOf(c));
  }

  public void testCopyOf_multiset_empty() {
    Multiset<String> c = HashMultiset.create();
    Multiset<String> multiset = ImmutableSortedMultiset.copyOf(c);
    assertTrue(multiset.isEmpty());
  }