Dereference of potentially null field

If the field is actually null, then a null pointer dereference will occur. Field, which is statistically checked against null, is dereferenced.
/src/mongo/db/pipeline/window_function/spillable_cache.cpp:115: NULL_FIELD 175278 Reading field "_diskCache", which is expected to possibly be "nullptr" in "this->_diskCache" (checked 4 out of 5 times).
/src/mongo/db/pipeline/window_function/spillable_cache.cpp:115: NULL_FIELD 175278 Attempting to access the managed object of an empty smart pointer "this->_diskCache".