code: public static <T> Optional<T> fromNullable(@Nullable T nullableReference) {
      return (nullableReference == null) ? Optional.<T>absent() : new Present<T>(nullableReference);
    }
docs: If {@code nullableReference} is non-null, returns an {@code Optional} instance containing that
  reference; otherwise returns {@link Optional#absent}.
  
  <p><b>Comparison to {@code java.util.Optional}:</b> this method is equivalent to Java 8's
  {@code Optional.ofNullable}.