How to use filter for not null in child table

I have a case where I want to restrict the filter to where data is not null.

cur_frm.fields_dict['sales_order_custom_parts'].grid.get_field('alternate_option').get_query = function(doc, cdt, cdn) {
var d =locals[cdt][cdn];
	return {
		['Item Alternate', 'parent', '=', d.item_code],
		['Item Alternate', 'item_code', 'is not', NULL]

Does anyone have any idea about it?

Ruchin Sharma

Have you tried this

['Item Alternate', 'item_code', '!=', null]