RFC 8259 describes these possibilities, accurately quoted in the article: "Many implementations report the last name/value pair only. Other implementations repo

RFC 8259 describes these possibilities, accurately quoted in the article: "Many implementations report the last name/value pair only. Other implementations report an error or fail to parse the object, and some implementations report all of the name/value pairs, including duplicates." Keeping the first key/value would be a poor idea since it is a behavior not mentioned in the RFC.