Not able to remove all vms from cluster group

[edubois10]

In the documentation, for govc cluster.group.change the following example is provided to add, remove vms from a given topic.

Examples:
  govc cluster.group.change -name my_group vm_a vm_b vm_c # set
  govc cluster.group.change -name my_group vm_a vm_b vm_c $(govc cluster.group.ls -name my_group) vm_d # add
  govc cluster.group.ls -name my_group | grep -v vm_b | xargs govc cluster.group.change -name my_group vm_a vm_b vm_c # remove

To be honest, I don't find this example helpful, it is not clear why we need to use $(govc cluster.group.ls -name my_group) when the command will list the existing vms in the group.

Let's say my Group has vm_a in it, and I want to add vm_b; what I do is govc cluster.group.change -name my_group vm_a vm_b if I want to remove vm_a, what I do is govc cluster.group.change -name my_group vm_b. After running the two commands, my group has only vm_b. My question is, how do I remove vm_b and therefore have an empty group? I tried by just doing govc cluster.group.change -name my_group but it is not working. Neither govc cluster.group.change -name my_group "" or ''

How should I proceed to remove all the vms from a Group?

Thank you for your help.