`geom_bkde2d` fails with `"argument 'z.range' is missing"` warning

[IndrajeetPatil]

I can't reproduce the output shown in {ggalt} vignette.

Expected:

Observed:

library(ggplot2)
library(ggalt)

m <- ggplot(faithful, aes(x = eruptions, y = waiting)) +
  geom_point() +
  xlim(0.5, 6) +
  ylim(40, 110)

m + geom_bkde2d(bandwidth = c(0.5, 4))

^{Created on 2021-08-15 by the reprex package (v2.0.1)}