Cost Center value is not fetching in filter

Dear All,

I am trying to add a filter for both cost center and workflow approval . cost center will be select in the link field cost_center, but it is showing none and only workflow state filter is working

frappe.ui.form.on(“Site Daily Expense”, “refresh”, function(frm) {
var cst_name = frm.doc.cost_center;
frm.set_query(“site_expense_number”, function() {
return {
“filters”: {
‘workflow_state’: “Approved”,
‘cost_center’: cst_name