Need to make group parent field as empty via flow

[Sanjeev001]

Requirement is to remove the parent of a group via flow 
I'm getting the group name in a reference catalog variable and I already tried few things 
1. Returning empty value  

2. Setting flow variable as empty and assigning that variable to parent 

3. Leaving value as empty 

[Sanjeev01]

In 3 leave value as empty 

I tried this only I was not working