Map a catalog item:s reference variable to sc_req_item:s "configuration_item" field in Back-end.

Hello guys!

I'm trying to map a reference variable called 'pr_number' (based on alm_asset) to a sc_req_item field called 'configuration_item' in Back-end. 

I have a workflow connected to my catalog item with this reference variable called pr_number. 

This is the script I use: 

else if (current.variables.pr_number) { current.configuration_item = current.variables.pr_number.cmdb_ci; // Map pr_number to configuration_item }

The problem is that it is always empty. Is there anything I've missed? It should be possible to dot-walk right?