In some cases it is possible to query for the undefined type. If full document matching is bypassed, such a query can match an empty array, which is stored in the index using the undefined type.
> c.ensureIndex( { a:1 } )
> c.save( { a:[] } )
> c.find( { a:{ $in:[ undefined ] } } )
{ "_id" : ObjectId("4f7a117c37365e9167f24ed3"), "a" : [ ] }
>
- is related to
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SERVER-1160 {a: undefined} broken with index
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- Closed
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SERVER-12024 re-implement $in in terms of $or
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- Backlog
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- Closed
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