Dereference null return value

If the function actually returns a null value, a null pointer dereference will occur. Return value of function which returns null is dereferenced without checking
/src/mongo/db/query/ce/ce_histogram.cpp:75: NULL_RETURNS 122917 Dereferencing a pointer that might be "nullptr" "key._path.cast()->name()" when calling "basic_string". [Note: The source code implementation of the function has been overridden by a builtin model.]