In file included from /in/compile/Dlist.h:80:0,
                 from /in/compile/dlist_driver.cpp:6:
/in/DlistImpl.h: In instantiation of 'Dlist<T>& Dlist<T>::operator=(const Dlist<T>&) [with T = int]':
/in/compile/dlist_driver.cpp:213:13:   required from here
/in/DlistImpl.h:99:27: error: invalid initialization of non-const reference of type 'Dlist<int>&' from an rvalue of type 'std::nullptr_t'
     if (isEmpty()) return nullptr;
                           ^~~~~~~
/in/compile/Makefile:10: recipe for target 'buildDlist' failed
make: *** [buildDlist] Error 1