Return value of function which returns null is dereferenced without checking

Defect 104960 (STATIC_C)
Checker NULL_RETURNS (subcategory none)
File: /src/mongo/db/operation_context_session_mongod.cpp
Function mongo::OperationContextSessionMongod::OperationContextSessionMongod(mongo::OperationContext *, bool, boost::optional<bool>, boost::optional<bool>)
/src/mongo/db/operation_context_session_mongod.cpp, line: 48
Assigning: "txnParticipant" = null return value from "get".

            auto txnParticipant = TransactionParticipant::get(opCtx);