*
   * <p>The multimap supports mapping removal, which removes the corresponding mapping from the map.
   * It does not support any operations which might add mappings, such as {@code put}, {@code
   * putAll} or {@code replaceValues}.
   *
   * <p>The returned multimap will be serializable if the specified map is serializable.
   *

      ListenableFuture<? extends V>... futures) {
    /*
     * Another way to express this signature would be to bound <V> by @NonNull and accept
     * LF<? extends @Nullable V>. That might be better: There's currently no difference between the
     * outputs users get when calling this with <Foo> and calling it with <@Nullable Foo>. The only

            "five", 5,
            "six", 6,
            "seven", 7,
            "eight", 8),
        "one",
        1,
        "two",
        2,
        "three",
        3,
        "four",
        4,
        "five",
        5,
        "six",
        6,
        "seven",
        7,
        "eight",
        8);
    assertMapEquals(
        ImmutableMap.of(
            "one", 1,