code: public Observable<ServiceResponse<KeyPhraseBatchResult>> keyPhrasesWithServiceResponseAsync(List<MultiLanguageInput> documents) {
          if (this.client.azureRegion() == null) {
              throw new IllegalArgumentException("Parameter this.client.azureRegion() is required and cannot be null.");
          }
          Validator.validate(documents);
          MultiLanguageBatchInput input = new MultiLanguageBatchInput();
          input.withDocuments(documents);
          String parameterizedHost = Joiner.on(", ").join("{AzureRegion}", this.client.azureRegion());
          return service.keyPhrases(this.client.acceptLanguage(), input, parameterizedHost, this.client.userAgent())
              .flatMap(new Func1<Response<ResponseBody>, Observable<ServiceResponse<KeyPhraseBatchResult>>>() {
                  @Override
                  public Observable<ServiceResponse<KeyPhraseBatchResult>> call(Response<ResponseBody> response) {
                      try {
                          ServiceResponse<KeyPhraseBatchResult> clientResponse = keyPhrasesDelegate(response);
                          return Observable.just(clientResponse);
                      } catch (Throwable t) {
                          return Observable.error(t);
                      }
                  }
              });
      }
docs: The API returns a list of strings denoting the key talking points in the input text.
  See the &lt;a href="https://docs.microsoft.com/en-us/azure/cognitive-services/text-analytics/overview#supported-languages"&gt;Text Analytics Documentation&lt;/a&gt; for details about the languages that are supported by key phrase extraction.
  
  @param documents the List&lt;MultiLanguageInput&gt; value
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the KeyPhraseBatchResult object