@Override public V get(Object o) {
    if (o == null) return null; // null keys are not allowed
    int i = arrayIndexOfKey(o);
    return i != -1 ? value(i + 1) : null;
  }
@Test void someNullValues() {
    array[0] = "1";
    array[1] = "one";
    array[2] = "2";
    array[3] = "two";
    array[4] = "3";

    Map<String, String> map = builder.build(array);
    assertSize(map, 2);
    assertBaseCase(map);

    assertThat(map).containsOnly(
        entry("1", "one"),
        entry("2", "two")
    );
    assertThat(map).hasToString(
        "UnsafeArrayMap{1=one,2=two}"
    );

    assertThat(map.get("1")).isEqualTo("one");
    assertThat(map.get("2")).isEqualTo("two");
    assertThat(map.get("3")).isNull();
  }