In UI namespace
(defprotocol CRUD
  "Create/read/update/delete operations on katello entities via the UI"
  (create [x] "Create an entity in the UI")
  (read [x] "Get details on an entity from the UI")
  (update* [x new-x] "Change an existing entity in UI, from x to new-x")
  (delete [x] "Delete an existing entity in the UI"))


In environments namespace.

(defn- create
  "Creates an environment with the given name, and a map containing
   the organization name to create the environment in, the prior
   environment, and an optional description."
  [{:keys [name label org description prior]}]
  (nav/go-to ::new-page org)
  (sel/fill-ajax-form {::name-text name
                       (fn [label] (when label
                                     (browser fireEvent ::name-text "blur")
                                     (browser ajaxWait)
                                     (browser setText ::label-text label))) [label]
                       ::description-text description
                       ::prior (:name prior)}
                      ::create)
  (notification/success-type :env-create))

(defn only-katello [task]
  (if (rest/is-headpin?)
        task
        ;; how to implement code for no-op??))

(extend katello.Environment
  ui/CRUD {:create (only-katello #'create)
           :update* edit
           :delete delete}


Question :-  What could I be missing in (only-katello function ?

Error faced :-   IllegalArgumentException No implementation of method: :create of protocol: #'katello.ui/CRUD found for class: katello.Environment  clojure.core/-cache-protocol-fn (core_deftype.clj:541)

While trying the beow.

=> (def env11 (first katello.conf/*environments*))
#'user/env11
=> env11
#katello.Environment{:id nil, :name "Development", :label nil, :description nil, :org #katello.Organization{:id nil, :name "ACME_Corporation", :label nil, :description nil, :initial-env nil}, :prior #katello.Environment{:id nil, :name "Library", :label nil, :description nil, :org #katello.Organization{:id nil, :name "ACME_Corporation", :label nil, :description nil, :initial-env nil}, :prior nil, :next nil}, :next nil}
=> (katello.ui/create env11)
IllegalArgumentException No implementation of method: :create of protocol: #'katello.ui/CRUD found for class: katello.Environment  clojure.core/-cache-protocol-fn (core_deftype.clj:541)