code: public PersistedFace addFaceFromUrl(String faceListId, String url, AddFaceFromUrlOptionalParameter addFaceFromUrlOptionalParameter) {
          return addFaceFromUrlWithServiceResponseAsync(faceListId, url, addFaceFromUrlOptionalParameter).toBlocking().single().body();
      }
docs: Add a face to a face list. The input face is specified as an image with a targetFace rectangle. It returns a persistedFaceId representing the added face, and persistedFaceId will not expire.
  
  @param faceListId Id referencing a particular face list.
  @param url Publicly reachable URL of an image
  @param addFaceFromUrlOptionalParameter the object representing the optional parameters to be set before calling this API
  @throws IllegalArgumentException thrown if parameters fail the validation
  @throws APIErrorException thrown if the request is rejected by server
  @throws RuntimeException all other wrapped checked exceptions if the request fails to be sent
  @return the PersistedFace object if successful.