code: @Override
      protected void serializeNullValue( JsonWriter writer, JsonSerializationContext ctx, JsonSerializerParameters params ) {
          if ( writer.getSerializeNulls() ) {
              writer.setSerializeNulls( false );
              writer.nullValue();
              writer.setSerializeNulls( true );
          } else {
              writer.nullValue();
          }
      }
docs: {@inheritDoc}