The function should return a reference to an array containing the parent
classes in order. The names of the classes should be the result of calling
-C<HvENAME()> on the stash. The caller is responsible for incrementing the
-reference count of the array returned if it wants to keep the structure.
-Hence, if you have created a temporary value that you keep no pointer to,
-C<sv_2mortal()> to ensure that it is disposed of correctly. If you have
-cached your return value, then return a pointer to it without changing the
-reference count.
+C<HvENAME()> on the stash. In those cases where C<HvENAME()> returns null,
+C<HvNAME()> should be used instead.
+
+The caller is responsible for incrementing the reference count of the array
+returned if it wants to keep the structure. Hence, if you have created a
+temporary value that you keep no pointer to, C<sv_2mortal()> to ensure that
+it is disposed of correctly. If you have cached your return value, then
+return a pointer to it without changing the reference count.
=head1 Caching