geom_sf(show.legend = "polygon") leads to error "Error in `vec_slice()`"

Using geom_sf(..., show.legend = "polygon") throws an error, while the same code with show.legend = "point" or show.legend = "line" will work well (see reprex below)?

The error is:

#> Error in vec_slice():
#> ! x must be a vector, not NULL.
#> ℹ Read our FAQ about scalar types (?vctrs::faq_error_scalar_type) to learn more.

library(ggplot2)
nc <- sf::st_read(system.file("shape/nc.shp", package = "sf"), quiet = TRUE)

nc$const_var <- "a"

ggplot(nc) +
  geom_sf(aes(fill = const_var), show.legend = "polygon")
#> Error in `vec_slice()`:
#> ! `x` must be a vector, not `NULL`.
#> ℹ Read our FAQ about scalar types (`?vctrs::faq_error_scalar_type`) to learn more.
ggplot(nc) +
  geom_sf(aes(fill = const_var), show.legend = "point")

ggplot(nc) +
  geom_sf(aes(fill = const_var), show.legend = "line")

^{Created on 2026-02-09 with reprex v2.1.1}

Start by running the supplied R reprex with sf and geom_sf, then trace the geom_sf legend handling for show.legend = "polygon" and compare it with the working point and line cases. Done means the polygon example no longer raises the vec_slice() error while the existing point and line behavior remains working.