Cell<@Nullable String, @Nullable Integer, @Nullable Character> nullEntry =
        immutableCell(null, null, null);
    assertEquals("(null,null)=null", nullEntry.toString());
  }

  public void testEntryEquals() {
    Cell<String, Integer, Character> entry = immutableCell("foo", 1, 'a');

    new EqualsTester()
        .addEqualityGroup(entry, immutableCell("foo", 1, 'a'))
        .addEqualityGroup(immutableCell("bar", 1, 'a'))