Dereference after null check

Either the check against null is unnecessary, or there may be a null pointer dereference. Pointer is checked against null but then dereferenced anyway
/src/mongo/db/query/query_solution.cpp:300: FORWARD_NULL 122808 Calling "this->_root.operator bool()" implies that "this->_root" might be null-like.
/src/mongo/db/query/query_solution.cpp:305: FORWARD_NULL 122808 Attempting to access the managed object of an empty smart pointer "this->_root".