code: public static <T> Optional<T> ofNullable(T value) {
          return value == null ? empty() : of(value);
      }
docs: Returns an {@code Optional} describing the specified value, if non-null,
  otherwise returns an empty {@code Optional}.
  
  @param <T> the class of the value
  @param value the possibly-null value to describe
  @return an {@code Optional} with a present value if the specified value
  is non-null, otherwise an empty {@code Optional}