In my opinion, it is slightly misleading, at least to humans, to use
the term “error” as the name of the error function. A better
term would be “cancel”. Strictly speaking, of course, you cannot
point to, much less rotate a pointer to a list that has no length, so
from the point of view of the computer, the word “error” is correct.
But a human expects to attempt this sort of thing, if only to find out
whether the kill ring is full or empty. This is an act of
exploration.
From the human point of view, the act of exploration and discovery is not necessarily an error, and therefore should not be labeled as one, even in the bowels of a computer. As it is, the code in Emacs implies that a human who is acting virtuously, by exploring his or her environment, is making an error. This is bad. Even though the computer takes the same steps as it does when there is an error, a term such as “cancel” would have a clearer connotation.