code: public Mono<Response<ConfigurationSetting>> getSetting(String key) {
          return getSetting(new ConfigurationSetting().key(key));
      }
docs: Attempts to get a ConfigurationSetting that matches the {@code key}.
  
  @param key The key of the setting to retrieve.
  @return The {@link ConfigurationSetting} stored in the service, or {@code null}, if the configuration value does
  not exist or the key is an invalid value (which will also throw ServiceRequestException described below).
  @throws IllegalArgumentException If {@code key} is {@code null}.
  @throws ServiceRequestException If the {@code key} and {@code label} does not exist. Or, if {@code key} is an
  empty string.