code: public Option<Either<L, R>> filter(Predicate<R> predicate) {
          return Option.apply(exists(predicate) ? either : null);
      }
docs: Returns a {@link Some} wrapping the {@link Either} if it's a {@link Right} and the value of the {@link Right} matches the predicate, else {@link None} .
  
  @param predicate
  The predicate to apply
  @return The resulting Option of the filter operation
  @since 1.1