[{"collection":"collection","count":5,"content":{"email":{"type":"fromArray","in":["foo","bar","demo","john","test"]}},"indexes":[{"name":"email_1","key":{"email":1},"partialFilterExpression":{"email":{"$type":2}}}]}]

db.collection.find({"email":{$eq:"foo",$type:"string"}}).explain("executionStats")