A reference can not be NULL or it can be NULL?

Question

I have read from the Wikipedia that:

“References cannot be null, whereas pointers can; every reference refers to some object, although it may or may n

Answer 1

clang 3.5 even warns on a possible later NULL check of a reference:

/tmp/person.C:11:6: warning: reference cannot be bound to dereferenced null pointer in well-defined C++ code; pointer may be assumed to
      always convert to true [-Wundefined-bool-conversion]
if (&object1) {}
~~   ^~~~~~~
1 warning generated.