code: public Observable<ServiceResponse<KeyPhraseBatchResult>> keyPhrasesWithServiceResponseAsync(KeyPhrasesOptionalParameter keyPhrasesOptionalParameter) {
          if (this.client.azureRegion() == null) {
              throw new IllegalArgumentException("Parameter this.client.azureRegion() is required and cannot be null.");
          }
          final List<MultiLanguageInput> documents = keyPhrasesOptionalParameter != null ? keyPhrasesOptionalParameter.documents() : null;
  
          return keyPhrasesWithServiceResponseAsync(documents);
      }
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 keyPhrasesOptionalParameter the object representing the optional parameters to be set before calling this API
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the KeyPhraseBatchResult object