Database
[{"Item":{"NestedItem":{"Id":"f4421f9e-5962-4c68-8049-a45600f36f4b","OtherId":"d6b799dc-f464-4919-8435-a7b600cc408a"},}},{"Item":{"NestedItem":{"Id":"f4421f9e-5962-4c68-8049-a45600f36f4b","OtherId":"d6b799dc-f464-4919-8435-a7b600cc408a"},}}]
Query
db.collection.aggregate([{$match:{$expr:{$or:[{$eq:[{$cond:[{$eq:["$Item.NestedItem",null]},null,"$Item.NestedItem.Id"]},"f4421f9e-5962-4c68-8049-a45600f36f4b"]},{$eq:[{$cond:[{$eq:["$Item.NestedItem",null]},null,"$Item.NestedItem.OtherId"]},"d6b799dc-f464-4919-8435-a7b600cc408a"]}]}}}])