sum filter nan mongodb aggregate

sum filter nan mongodb aggregate

db.getCollection("fb_report_detail").aggregate([
{"$match":{
    "campaign_id":{"$in":["23852528555800329"]},
    "adset_id":{"$in":["23852528555870329","23852661751140329"]}}},
    { '$group': {
            '_id': '$ad_id',
            'inline_link_clicks': { 
                '$sum': {
                    '$cond': [
                        { '$eq': ['$inline_link_clicks', NaN]}, 
                        0,
                        '$inline_link_clicks'
                    ]
                }
            }
        }},
        
        ])