code: public <T> Exception onError(HystrixInvokable<T> commandInstance, FailureType failureType, Exception e) {
          return e; //by default, just pass through
      }
docs: Invoked when {@link HystrixInvokable} fails with an Exception.
  
  @param commandInstance The executing HystrixInvokable instance.
  @param failureType {@link FailureType} enum representing which type of error
  @param e exception object
  
  @since 1.2