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    Type:Bug 
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    Resolution: Duplicate
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    Priority:Major - P3 
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    Affects Version/s: 4.2.1
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    Component/s: Aggregation Framework
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The assert in https://github.com/mongodb/mongo/blob/master/src/mongo/db/pipeline/expression.cpp fires at line starting from "uassert(51156"
The comment to the code mentions "The latter scenario should never occur" but it does 
- duplicates
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                    SERVER-44617 $regexFind crash when one of the capture group doesn't match the input but pattern matches -         
- Closed
 
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