code: @Override
      public ListSubscriptionDefinitionsResult listSubscriptionDefinitions(ListSubscriptionDefinitionsRequest request) {
          request = beforeClientExecution(request);
          return executeListSubscriptionDefinitions(request);
      }
docs: Retrieves a list of subscription definitions.
  
  @param listSubscriptionDefinitionsRequest
  @return Result of the ListSubscriptionDefinitions operation returned by the service.
  @sample AWSGreengrass.ListSubscriptionDefinitions
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/greengrass-2017-06-07/ListSubscriptionDefinitions"
  target="_top">AWS API Documentation</a>