This was suggested here: cmu-delphi/covidcast#669 (comment)

We can either check later in the plot building progress whether this is the case, e.g. in Geom$use_defaults() or demote from warning to message.

library(ggplot2)

ggplot(mpg[0,], aes(displ, hwy)) +
  geom_point(colour = NULL)
#> Warning in geom_point(colour = NULL): Ignoring empty aesthetic: `colour`.

^{Created on 2025-06-26 with reprex v2.1.1}