// Inheritance is closed, and all subtypes are @DoNotCall, so this is safe to suppress.
  @SuppressWarnings("DoNotCall")
  public ImmutableCollection<V> replaceValues(K key, Iterable<? extends V> values) {
    throw new UnsupportedOperationException();
  }

  /**
   * Guaranteed to throw an exception and leave the multimap unmodified.
   *

    checkNotNull(type);
    checkNotNull(value1);
    checkNotNull(value2);
    checkArgument(!Objects.equals(value1, value2), "Duplicate value provided.");
    distinctValues.replaceValues(type, ImmutableList.of(value1, value2));
    setDefault(type, value1);
    return this;
  }

  /**
   * Tests that {@code cls} properly checks null on all constructor and method parameters that