Projection parse(boost::intrusive_ptr<ExpressionContext> expCtx,
                 const BSONObj& obj,
                 ProjectionPolicies policies) {
    return parse(std::move(expCtx), obj, nullptr, BSONObj(), std::move(policies));
}
Projection parse(boost::intrusive_ptr<ExpressionContext> expCtx,
                 const BSONObj& obj,
                 ProjectionPolicies policies) {
    return parse(std::move(expCtx), obj, nullptr, BSONObj(), std::move(policies));
}