code: @Override
      public ListFunctionsResult listFunctions(ListFunctionsRequest request) {
          request = beforeClientExecution(request);
          return executeListFunctions(request);
      }
docs: <p>
  List multiple functions.
  </p>
  
  @param listFunctionsRequest
  @return Result of the ListFunctions operation returned by the service.
  @throws BadRequestException
  The request is not well formed. For example, a value is invalid or a required field is missing. Check the
  field values, and then try again.
  @throws NotFoundException
  The resource specified in the request was not found. Check the resource, and then try again.
  @throws UnauthorizedException
  You are not authorized to perform this operation.
  @throws InternalFailureException
  An internal AWS AppSync error occurred. Try your request again.
  @sample AWSAppSync.ListFunctions
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/appsync-2017-07-25/ListFunctions" target="_top">AWS API
  Documentation</a>