code: public void runDecider(String workflowId) {
          Preconditions.checkArgument(StringUtils.isNotBlank(workflowId), "workflow id cannot be blank");
          stub.decideWorkflow(WorkflowServicePb.DecideWorkflowRequest.newBuilder()
                  .setWorkflowId(workflowId)
                  .build()
          );
      }
docs: /*
  Starts the decision task for the given workflow instance
  
  @param workflowId the id of the workflow instance