Return value of function which returns null is dereferenced without checking

Defect 99343 (STATIC_C)
Checker NULL_RETURNS (subcategory none)
File: /src/mongo/db/query/stage_builder.cpp
Function mongo::buildStages(mongo::OperationContext *, mongo::Collection *, const mongo::CanonicalQuery &, const mongo::QuerySolution &, const mongo::QuerySolutionNode *, mongo::WorkingSet *)
/src/mongo/db/query/stage_builder.cpp, line: 308
Assigning: "params.descriptor" = null return value from "findIndexByKeyPattern".

            params.descriptor =

File: /src/mongo/db/query/stage_builder.cpp
Function mongo::buildStages(mongo::OperationContext *, mongo::Collection *, const mongo::CanonicalQuery &, const mongo::QuerySolution &, const mongo::QuerySolutionNode *, mongo::WorkingSet *)
/src/mongo/db/query/stage_builder.cpp, line: 324
Assigning: "params.descriptor" = null return value from "findIndexByKeyPattern".

            params.descriptor =