message: Documented `oatpp::parser::json::mapping::Serializer::Config::alwaysIncludeRequired` in changelog.
diff: @@ -14,6 +14,7 @@ Contents:
  - [Response::getBody()](#responsegetbody)
  - [data::stream::FIFOStream](#datastreamfifostream)
  - [data::stream::BufferedInputStream](#datastreambufferedinputstream)
  +- [oatpp::parser::json::mapping::Serializer::Config::alwaysIncludeRequired](#oatppparserjsonmappingSerializerConfigalwaysIncludeRequired)
  ## The New oatpp::String
  @@ -199,7 +200,8 @@ ENDPOINT("GET", "videos/{videoId}", getVideoById,
  ## Response::getBody()
  -`oatpp::web::protocol::http::outgoing::Response` has a new method `getBody()` to retreive the body of the response. This is handy for response interceptors.
  +`oatpp::web::protocol::http::outgoing::Response` has a new method `getBody()` to retreive the body of the response.
  +This is handy for response interceptors.
  ## data::stream::FIFOStream
  @@ -223,3 +225,33 @@ You need to implement your own locking.
  [`BufferedInputStream`](https://oatpp.io/api/latest/oatpp/core/data/stream/Stream/#bufferedinputstream) which unifies
  the bufferd-stream-interface all existing buffered streams (`InputStreamBufferedProxy`, `BufferInputStream`,
  `FIFOStream`) to allow for generalisation.
  +
  +## oatpp::parser::json::mapping::Serializer::Config::alwaysIncludeRequired
  +
  +If `oatpp::parser::json::mapping::Serializer::Config::includeNullFields == false` there might still be the requirement
  +to include some fields even if they are `nullptr`, because they are required by the deserializing end.
  +
  +Consider the following DTO and endpoint-snippet.
  +```c++
  +class StatusDto : public oatpp::DTO {
  + DTO_INIT(StatusDto, DTO)
  + DTO_FIELD_INFO(status) {
  + info->required = true;
  + }
  + DTO_FIELD(String, status);
  + DTO_FIELD(Int32, code);
  + DTO_FIELD(String, message);
  +};
  +
  +// endpoint code:
  +ENDPOINT("GET", "/status", status) {
  + auto dto = StatusDto::createShared();
  + dto->code = 200;
  + return createDtoResponse(Status::CODE_200, dto);
  +}
  +```
  +With a serializer with its config set to `Serializer::Config::includeNullFields = false`, the snippet would just yield `{"code":200}`.
  +
  +However, `status` is a required field.
  +Now, one can set `Serializer::Config::alwaysIncludeRequired = true`.
  +With `alwaysIncludeRequired == true`, the same snippet would yield `{"status":null,"code":200}`, even with `includeNullFields == false`.
  