_assign field set value

frm.set_value(‘_assign’, ‘e1@example.com’);
I tried this line to add value to _assign field in Issue doctype.
but i get message that _assign field is not there.

what should i do ? any help please?

I did it by creating new todo document like this: (in Purchase Order)
doctype: ‘ToDo’, description:‘This is test auto create’,
reference_type: ‘Purchase Order’, reference_name: cur_frm.doc.name, allocated_to: “e1@example.com
You can examine by manualy assigning user to your doctype and see what is created on ToDo document.
important field are: description, reference_type, reference_name and allocated_to
I hope this will help.