code: public Mono<Response<ConfigurationSetting>> deleteSetting(String key) {
          return deleteSetting(new ConfigurationSetting().key(key));
      }
docs: Deletes the ConfigurationSetting with a matching {@code key}.
  
  @param key The key of the setting to delete.
  @return The deleted ConfigurationSetting or {@code null} if it didn't exist. {@code null} is also returned if
  the {@code key} is an invalid value (which will also throw ServiceRequestException described below).
  @throws IllegalArgumentException If {@code key} is {@code null}.
  @throws ServiceRequestException If {@code key} is an empty string.