code: public Mono<Response<ConfigurationSetting>> deleteSetting(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.delete(serviceEndpoint, setting.key(), setting.label(), getETagValue(setting.etag()), null);
      }
docs: Deletes the {@link ConfigurationSetting} with a matching key, along with the given label and etag.
  
  If {@link ConfigurationSetting#etag() etag} is specified and is not the wildcard character ({@code "*"}),
  then the setting is <b>only</b> deleted if the etag matches the current etag; this means that no one has updated
  the ConfigurationSetting yet.
  
  @param setting The ConfigurationSetting to delete.
  @return The deleted ConfigurationSetting or {@code null} if didn't exist. {@code null} is also returned if
  the {@code key} is an invalid value or {@link ConfigurationSetting#etag() etag} is set but does not match the
  current etag (which will also throw ServiceRequestException described below).
  @throws IllegalArgumentException If {@link ConfigurationSetting#key() key} is {@code null}.
  @throws NullPointerException When {@code setting} is {@code null}.
  @throws ServiceRequestException If {@code key} is an empty string or {@link ConfigurationSetting#etag() etag} is
  specified, not the wildcard character, and does not match the current etag value.