str_c() and missing values

df <- tibble(name = c("Flora", "David", NA))
df |> 
  mutate(
    greeting0 = str_c("Hi ", name, "!"),
    greeting1 = str_c("Hi ", coalesce(name, "you"), "!"),
    greeting2 = coalesce(str_c("Hi ", name, "!"), "Hi!")
  )

## # A tibble: 3 × 4
##   name  greeting0 greeting1 greeting2
##   <chr> <chr>     <chr>     <chr>    
## 1 Flora Hi Flora! Hi Flora! Hi Flora!
## 2 David Hi David! Hi David! Hi David!
## 3 <NA>  <NA>      Hi you!   Hi!