## Motivation Operator register api of v2 can remove the part that passes `null` as a parameter through method overloading. In this case, we can remove the logic to protect null from the logic inside the register api. This can make register api code more readable. ## Proposal * Change deprecated `kubernetesClient.getVersion` to `KubernetesClient.getKubernetesVersion` * Pass a non-null value as a parameter by creating `defaultConfiguration` in register(Reconciler<R> reconciler) * Remove unnecessary null defense code