code: public static <T1, T2> Serializer<Tuple2<T1, T2>> serializer( Serializer<T1> first,
                                                                    Serializer<T2> second ) {
          return new Tuple2Serializer<>(first, second);
      }
docs: Create a {@link Serializer} for tuples of size 2.
  
  @param first the serializer for the first slot
  @param second the serializer for the second slot
  @return the serializer; never null