It occurs when you chain methods and one of them returns 'undef' - or when you just call methods on an undefined value.
perl -e 'undef->x'
If "$a->b->c" throws this message you can rewrite it as "$a->b && $a->b->c". But how boring is this?
Scalar::Andand to the rescue! Now you can write "$a->b->andand->c".
It's important to quote the documentation:
Note that this module was intended as a proof of concept. The author has never used it in production code, nor is he planning to do so.
I continue tomorrow with "serious" stuff. :)