[chef] How to detect user does exist?

[Anthony Kong < >]

Hi 

I have this definition on my cookbook

group "sensu" do

  action :modify

  members "vagrant"

  append true

end

it will throw an exception when I run it on ec2 because there is no user vagrant

How can I avoid the exception? Is there any way to detect the user exist? I have checked the doc https://docs.chef.io/resource_group.html but there is nothing obvious

Cheers,