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Type:
Bug
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Resolution: Fixed
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Priority:
Major - P3
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Affects Version/s: None
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Component/s: Aggregation Framework
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Minor Change
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ALL
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Query 2019-09-23, Query 2019-10-07
> db.foo.find()
{ "_id" : 2 }
{ "_id" : 1, "x" : null }
{ "_id" : 3, "y" : null }
{ "_id" : 4, "x" : null, "y" : null }
> db.foo.aggregate([{$group: {_id: ["$x", "$y"]}}])
{ "_id" : [ "$x", "$y" ] }
> db.foo.aggregate([{$group: {_id: {z: ["$x", "$y"]}}}])
{ "_id" : { "z" : [ null, null ] } }
I would contend that the middle one should result in
{_id: [null, null]}
Looks like this is the offending line.