Database
[{"_id":206,"Events":[{"_t":"PageReviewed","UpdateDate":null},{"_t":"PageMetadataSet","UpdateDate":null,"Metadata":{"Category":"Any caSE cateGory","Name":"Any CaSe name","Culture":"*","Environment":"*","Platform":"*","Value":true,"ValueTypeName":"System.Boolean"}}]},{"_id":207,"Events":[{"_t":"PageReviewed","UpdateDate":null},{"_t":"PageMetadataSet","UpdateDate":null,"Metadata":{"Category":"Any casing Category","Name":"Any casing Name","Culture":"*","Environment":"*","Platform":"*","Value":false,"ValueTypeName":"System.Boolean"}}]}]
Query
db.collection.aggregate([{$project:{"Events_orid":"$Events",newField:{$map:{input:"$Events",as:"thisEvent",in:{$cond:[{$gt:["$$thisEvent.Metadata.Name",null]},{$mergeObjects:["$$thisEvent",{"Metadata":{$mergeObjects:["$$thisEvent.Metadata",{"Name":{$toLower:"$$thisEvent.Metadata.Name"}}]}}]},"$$thisEvent"]}}}}}])