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    Type:Bug 
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    Resolution: Works as Designed
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    Priority:Major - P3 
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    Affects Version/s: 3.2.3
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    Component/s: Querying
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        ALL
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When execute
{ $setUnion: { [ "a", "b", "c" ], [ "b", "a", "a", "d" ]  }}
or
either returns: "b", "a", "a", "d"
1. union does not work. expected result for union should include: "c", "b", "a", "d"
2. duplicated items do not removed from the result.