PyWeakref_GetObject returns None (not NULL) when the referent is gone.

Doc/api/concrete.tex

@@ -2409,7 +2409,7 @@ acts as a proxy for the original object as much as it can.
 
 \begin{cfuncdesc}{PyObject*}{PyWeakref_GetObject}{PyObject *ref}
   Returns the referenced object from a weak reference, \var{ref}.  If
-  the referent is no longer live, returns \NULL.
+  the referent is no longer live, returns \code{None}.
   \versionadded{2.2}
 \end{cfuncdesc}