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/s/migration_chunk_cloner_source.cpp:1184: NULL_FIELD 176610 Reading field "_sessionCatalogSource", which is expected to possibly be "nullptr" in "this->_sessionCatalogSource" (checked 10 out of 12 times).
/src/mongo/db/s/migration_chunk_cloner_source.cpp:1184: NULL_FIELD 176610 Attempting to access the managed object of an empty smart pointer "this->_sessionCatalogSource".