public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2) {
    Map<K, V> map = new HashMap<>(2);
    map.put(k1, v1);
    map.put(k2, v2);
    return Collections.unmodifiableMap(map);
  }
Utility class to create immutable maps.

<p>We do not replicate Guava's ImmutableMap class here. This class merely returns standard {@link
HashMap}s wrapped so that they throw UnsupportedOperationExceptions on any write method.
fbcore/src/main/java/com/facebook/common/internal/ImmutableMap.java