code: public Mono<Response<ConfigurationSetting>> getSetting(ConfigurationSetting setting) {
          // Validate that setting and key is not null. The key is used in the service URL so it cannot be null.
          validateSetting(setting);
  
          return service.getKeyValue(serviceEndpoint, setting.key(), setting.label(), null, null, null, null);
      }
docs: Attempts to get the ConfigurationSetting given the {@code key}, optional {@code label}.
  
  @param setting The setting to retrieve based on its key and optional label combination.
  @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 NullPointerException If {@code setting} is {@code null}.
  @throws IllegalArgumentException If {@link ConfigurationSetting#key() key} is {@code null}.
  @throws ServiceRequestException If a ConfigurationSetting with the same key and label does not exist, or the key
  is an empty string.