Should the shape scale `na.value` default to something?

[davidhodge931]

library(tidyverse)

p <- palmerpenguins::penguins |>
  ggplot() +
  geom_point(
    aes(x = flipper_length_mm, y = body_mass_g, colour = sex, shape = sex),
  )

p
#> Warning: Removed 11 rows containing missing values or values outside the scale range
#> (`geom_point()`).

p +
  scale_shape_discrete(na.value = 78)
#> Warning: Removed 2 rows containing missing values or values outside the scale range
#> (`geom_point()`).

^{Created on 2025-09-22 with reprex v2.1.1}

[teunbrand]

The answer to 'could it' is 'yes', but perhaps the bigger question is 'should it' (and if so, what should it be)?

[davidhodge931]

I think it should be something for similar reasons that colour/fill scales have it grey.

Not sure what it should be. Something a bit obscure probably..