> db.fuzzer_coll.explain().aggregate([{$match: {"array": {$exists: true}}}, {$count: "num" }])

[4] project [s13 = makeBsonObj(MakeObjSpec([\"num\"], Closed, ReturnNothing), s12)] 
[3] mkobj s12 [_id = s11, num = s9] true false 
[3] project [s11 = null] 
[3] group [] [s9 = sum(1)] spillSlots[s10] mergingExprs[sum(s10)] 
[2] block_to_row blocks[s5] row[s8] s7 
[2] project [s7 = valueBlockExists(cellBlockGetFlatValuesBlock(s6))] 
[2] ts_bucket_to_cellblock s3 pathReqs[s5 = Get(array)/Id, s6 = Get(array)/Traverse/Id] 
[1] filter {(traverseF(s2, lambda(l101.0) { traverseF(getField(move(l101.0), \"max\"), lambda(l102.0) { exists(getField(move(l102.0), \"array\")) }, false) }, false) && traverseF(s2, lambda(l103.0) { traverseF(getField(move(l103.0), \"min\"), lambda(l104.0) { exists(getField(move(l104.0), \"array\")) }, false) }, false))} 
[1] scan s3 s4 none none none none none none lowPriority [s2 = control] @\"dcc8f30a-4eb1-4e28-9d50-129c139ba23f\" true false