Set_if documentation wrong?!

Describe the bug

I try to implement the set_if functrion in one of my CheckCommands, but failed to succussed.
Orientation was the documentation found here Use Functions in Command Arguments set_if

I also describe my tests on the Icinga Community.

To Reproduce

example host:

object Host "s002.domain.net" {
    import "generic-agent"

    display_name = "s002"
    address = "xxx.xxx.240.12"
    zone = "xxx"
    vars.centos = {
        centos7 = {
            cluster = true
        }
    }
    vars.redhatel = true
    vars.redhatel7 = true
    vars.server = true
    vars.sys = {
        icinga2 = {
            client = true
            zone = {
                xxx = true
            }
        }
        infiniband = {
            mlx5_port1_100 = true
        }
        openssh = true
        platform_mpi = true
        prometheus = true
        racadm = true
        resolver = true
    }
    vars.vendor = {
        dell = {
            poweredge = {
                c6525 = true
            }
        }
    }
}

Example CheckCommand:

object CheckCommand "check_ib" {
  command   = [ "/usr/bin/check_ib" ]
  arguments   = {
    "--dev"  = {
      set_if = {{
        var host_vars = host.vars
        log(host_vars)
        var infiniband = host_vars.sys.infiniband
        log(infiniband)
        return infiniband.keys()
      }}
    }
  }
}

I was not able to get the hosts vars into the check command.
The variable host_vars was always empty logged.

Expected behavior

Documented examples should work.

Workaround / Possible Solution

Calling macro() when importing the vars:

object CheckCommand "check_ib" {
  command   = [ "/usr/bin/check_ib" ]
  arguments   = {
    "--dev"  = {
      set_if = {{
        var host_vars = macro("$host.vars$")
        log(host_vars)
        var infiniband = host_vars.sys.infiniband
        log(infiniband)
        return infiniband.keys()
      }}
    }
  }
}

Your Environment

Director version (System - About):1.9.0
Icinga Web 2 version and modules (System - About): 2.9.5
Icinga 2 version (icinga2 --version): 2.13.2-1
Operating System and version: RockyLinux 8
Webserver, PHP versions:
Apache 2.4.37-41
PHP 7.4.19

Start with the linked “Use Functions in Command Arguments set_if” documentation section and compare its example with the CheckCommand reproduction in this issue. Verify the behavior using the supplied host and command definitions, then update the documentation so the example accurately describes how host variables are accessed; done means the documented example works or clearly states the required workaround.