`Error: Must request at least one colour from a hue palette` when plotting `NA` values

[TimBMK]

When using the color or fill aesthetics on a variable with only NA values, this produces the following error:
Error: Must request at least one colour from a hue palette.

The obvious workaround is to replace the NA values with a different value, such as "none". However, I feel like the default grey color for NA should get assigned even when plotting only NA values, rather than forcing the user to assign a different color (or circle around and reassign grey for the no-longer-NA values). For me, this would be the expected behavior and helpful in such cases as plotting a large number of graphs in a loop (e.g. when making a markdown report), where some data subsets have only of NA values in the color/fill variable, while others don't.

This behavior might possibly be related to this issue (even though another solution was found there): #5555

Reprex:

data.frame(x = 1:10, y = 11:20, color = "NA") %>%  # this works as expected
    ggplot(aes(x = x, y = y, color = color)) +
    geom_line()

data.frame(x = 1:10, y = 11:20, color = NA) %>%  # this throws an error
    ggplot(aes(x = x, y = y, color = color)) +
    geom_line()

Note that the same can be observed for the fill aesthetic. geom_line() is merely there for illustrative purposes, as the error occurs in ggplot()

[teunbrand]

Thanks for the report, I can reproduce the bug and agree with you that the scale's na.value should be applied in this case.
I don't think the linked issue is closely related to this one.