code: private CompletableFuture<Void> apply(ConfigurationEntry entry) {
      // Clean the configuration entry from the log. The entry will be retained until it has been stored
      // on all servers.
      log.release(entry.getIndex());
      return CompletableFuture.completedFuture(null);
    }
docs: Applies a configuration entry to the internal state machine.
  <p>
  Configuration entries are applied to internal server state when written to the log. Thus, no significant
  logic needs to take place in the handling of configuration entries. We simply release the previous configuration
  entry since it was overwritten by a more recent committed configuration entry.