The latest Leiningen version 2.7.1 adds [org.clojure/tools.nrepl "0.2.12"] whereas lein-ring adds [org.clojure/tools.nrepl "0.2.3"] to the project dependencies, which causes conflict when running lein ring server-headless with nREPL config enabled and :pedantic? :abort entry in project.clj.

Please either allow a way to specify the tools.nrepl version to be used with lein-ring, or use the latest version synced with latest Leiningen.