Distinct over empty indexed arrays produces undefined value in the result

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    • Type: Bug
    • Resolution: Duplicate
    • Priority: Major - P3
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    • Affects Version/s: 3.4.9
    • Component/s: Querying
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      > db.testcol.insert({"someArray": ["1"]});
      WriteResult({ "nInserted" : 1 })
      > db.testcol.insert({"someArray": ["2"]});
      WriteResult({ "nInserted" : 1 })
      > db.testcol.insert({"someArray": []});
      WriteResult({ "nInserted" : 1 })
      > 
      > db.testcol.distinct("someArray")
      [ "1", "2" ]
      >
      > 
      > db.testcol.ensureIndex({"someArray": 1})
      {
      	"createdCollectionAutomatically" : false,
      	"numIndexesBefore" : 1,
      	"numIndexesAfter" : 2,
      	"ok" : 1
      }
      > 
      > db.testcol.distinct("someArray")
      [ undefined, "1", "2" ]
      
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      > db.testcol.insert({"someArray": ["1"]}); WriteResult({ "nInserted" : 1 }) > db.testcol.insert({"someArray": ["2"]}); WriteResult({ "nInserted" : 1 }) > db.testcol.insert({"someArray": []}); WriteResult({ "nInserted" : 1 }) > > db.testcol.distinct("someArray") [ "1", "2" ] > > > db.testcol.ensureIndex({"someArray": 1}) { "createdCollectionAutomatically" : false, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } > > db.testcol.distinct("someArray") [ undefined, "1", "2" ]
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      When using the distinct command targeting an indexed array field, which also happens to be empty, an additional `undefined` value is added to the result.

      If there is no index on the field, it's correct - there is no `undefined` value in the result.

              Assignee:
              Kelsey Schubert
              Reporter:
              Slavi Pantaleev
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                Created:
                Updated:
                Resolved: