}

  public void testAsConverter_withNullMapping() throws Exception {
    BiMap<String, @Nullable Integer> biMap = HashBiMap.create();
    biMap.put("one", 1);
    biMap.put("two", 2);
    biMap.put("three", null);
    try {
      Maps.asConverter((BiMap<String, Integer>) biMap).convert("three");
      fail();
    } catch (IllegalArgumentException expected) {
    }
  }

  }

  public void testAsConverter_withNullMapping() throws Exception {
    BiMap<String, @Nullable Integer> biMap = HashBiMap.create();
    biMap.put("one", 1);
    biMap.put("two", 2);
    biMap.put("three", null);
    try {
      Maps.asConverter((BiMap<String, Integer>) biMap).convert("three");
      fail();
    } catch (IllegalArgumentException expected) {
    }
  }

  }

  static <K extends @Nullable Object, V extends @Nullable Object> BiMap<K, V> biMap(
      BiMap<K, V> bimap, @CheckForNull Object mutex) {
    if (bimap instanceof SynchronizedBiMap || bimap instanceof ImmutableBiMap) {
      return bimap;
    }
    return new SynchronizedBiMap<>(bimap, mutex, null);
  }