A case where it raises an error with the new code

sage: x = SR.var("x")
....: f = (x^30).series(x, 20); f
Order(x^20)
sage: f.coefficients(x, sparse=True)
[[Order(x^20), 0]]

So another purpose of the overridden method is that it right-pad the coefficient list with zeroes on the right to match the Order. Otherwise some of the things that raise error in the new code does look like a bug.

Documentation preview for this PR (built with commit 35f5359; changes) is ready! 🎉
This preview will update shortly after each push to this PR.