* changed files from rebuilding project and updating samples
* change default value of from_encoding to empty string
- from_encoding = NULL is invalid and produces an error, as only strings are allowed, see https://www.rdocumentation.org/packages/base/versions/3.6.2/topics/iconv
- defaulting to an empty string fixes this issue
* fix map being surrounded by quotes in json
* allow httr2 client to deal with empty response body
* changed files from rebuilding project and updating samples
* added PetMap schema for test of correct map serialization in toJSONString and regenerated samples
* add discriminator property, mapping
* add discriminator, mapping support to R client generator
* add discriminator, mapping support to R client genrator httr library
