public static <K, V> Map<K, V> of() {
    return Collections.unmodifiableMap(new HashMap<K, V>());
  }
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