Starting in MongoDB 4.4, the ns field will no longer be present in the index specifications returned from the listIndexes server command. This affects drivers that return statically defined models of index specifications as part of their own listIndexes helpers, as well as drivers that document the contents of any loose documents/dictionaries they return from that helper instead. Such drivers may need to update their code and/or documentation as per the new changes to the index enumeration spec.
POCs: PHP - Andreas, .NET, Java
Relevant Spec Changes: In SPEC-1399, a new section was added to the index enumeration spec mentioning how drivers should handle this change. Also, new test scenarios were added to the test plan.