object 'fac' not found

Hello,

I've run the code below many times, though not recently. I received this error message, but the code runs.

> Error in FUN(X[[i]], ...) : object 'fac' not found

Instead of a white background, it is grey. If fac isn't a valid fill value, what is required?

Any assistance is appreciated.

Bob

library(tidyverse)
library(sf)
world_sf = map_data("world") %>% 
   filter(region != "Antarctica") %>%
   mutate(region=replace(region, subregion=="Alaska", "USA_Alaska")) %>% 
   st_as_sf(coords=c("long","lat"), crs=4326) %>%
   group_by(region, group) %>% summarise(geometry=st_combine(geometry)) %>%
   st_cast("POLYGON") %>% summarise(geometry=st_combine(geometry))

labs = tibble(region = c("Argentina", "Australia", "Barbados","Brazil", "England","Fiji", "France", "French Polynesia", "Ghana", "Italy","Japan", "New Zealand", "Papua New Guinea", "Peru", "Portugal", "Samoa", "Sao Tome and Principe", "Senegal", "Solomon Islands", "South Africa", "Spain", "Trinidad", "Tobago", "Turkey", "UK", "Uruguay", "USA"))
ggplot()+geom_sf(aes(fill=fac))+coord_sf(expand=FALSE)

labels_sf =  st_point_on_surface(world_sf) %>% right_join(labs, by="region")


world_sf %>% mutate(fac = region %in% labs$region)  %>%
   ggplot()+geom_sf(aes(fill=fac))+coord_sf( expand=FALSE)+
   theme(axis.title = element_blank(), legend.position = "none")+
   scale_fill_manual(values=c("FALSE"=NA, "TRUE"="red"))