code: public Observable<ServiceResponse<List<ExpressionRootInner>>> listExpressionTracesWithServiceResponseAsync(String resourceGroupName, String workflowName, String runName, String actionName) {
          if (this.client.subscriptionId() == null) {
              throw new IllegalArgumentException("Parameter this.client.subscriptionId() is required and cannot be null.");
          }
          if (resourceGroupName == null) {
              throw new IllegalArgumentException("Parameter resourceGroupName is required and cannot be null.");
          }
          if (workflowName == null) {
              throw new IllegalArgumentException("Parameter workflowName is required and cannot be null.");
          }
          if (runName == null) {
              throw new IllegalArgumentException("Parameter runName is required and cannot be null.");
          }
          if (actionName == null) {
              throw new IllegalArgumentException("Parameter actionName is required and cannot be null.");
          }
          if (this.client.apiVersion() == null) {
              throw new IllegalArgumentException("Parameter this.client.apiVersion() is required and cannot be null.");
          }
          return service.listExpressionTraces(this.client.subscriptionId(), resourceGroupName, workflowName, runName, actionName, this.client.apiVersion(), this.client.acceptLanguage(), this.client.userAgent())
              .flatMap(new Func1<Response<ResponseBody>, Observable<ServiceResponse<List<ExpressionRootInner>>>>() {
                  @Override
                  public Observable<ServiceResponse<List<ExpressionRootInner>>> call(Response<ResponseBody> response) {
                      try {
                          ServiceResponse<PageImpl1<ExpressionRootInner>> result = listExpressionTracesDelegate(response);
                          List<ExpressionRootInner> items = null;
                          if (result.body() != null) {
                              items = result.body().items();
                          }
                          ServiceResponse<List<ExpressionRootInner>> clientResponse = new ServiceResponse<List<ExpressionRootInner>>(items, result.response());
                          return Observable.just(clientResponse);
                      } catch (Throwable t) {
                          return Observable.error(t);
                      }
                  }
              });
      }
docs: Lists a workflow run expression trace.
  
  @param resourceGroupName The resource group name.
  @param workflowName The workflow name.
  @param runName The workflow run name.
  @param actionName The workflow action name.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the List&lt;ExpressionRootInner&gt; object