The aggregation with a single $match stage over timeseries

[{"$match" : {"$expr" : {"$getField" : "measurement1"}}}] 

is incorrectly pushed before the internalUnpackBucket stage and evaluated to an empty document set.

This happens in DocumentSource::PushMatchBefore() function where the analysis misses the fact that the $match stage needs the entire document. https://github.com/mongodb/mongo/blob/v5.0/src/mongo/db/pipeline/document_source.cpp#L199