The following document can't be inserted in a collection with Studio 3T :

{
"id" : ObjectId("5b16ade6540bd478204f08c4"),
"name" : "Extract all tags used",
"ticket": "GQ-53",
"modelQuery": "Customer",
"aggregateQuery": [
{
$unwind: '$tags'
},
{
$group: {
_id: '$tags',
count: { $sum: 1 }
}
},
{
$sort: {
count: -1
}
},
{
$project: {
_id: 0,
tag: '$id',
count: 1
}
}
],
}

The same document can be inserted with mongo shell.

PS: It's a valid document when mongod is at version 3.6 or more recent.