Function needed for a custom button that can close overdue activities in leads

Function needed for a custom button that can close overdue activities in leads

Hello.
I need a function for a custom button (List View - Mass Action Menu) that can close overdue activities in leads. 

I've tried this but the arguments are wrong apparently:

Argument:
leadId = Leads - lead Id

Function:

relactivities = zoho.crm.getRelatedRecords("Activities","Leads",leadId.toLong(),1);

for each rec in relactivities
{
if(rec.get("Activities") = "Overdue")
{
      closeResp = zoho.crm.invokeConnector("crm.close",{"module":"Activities","id":rec.get("id")});
      info closeResp;
}
}

I keep on getting the message:
Missing return statement: Provide STRING expression to return Line Number:1

Can someone help?