`complete()` doesn't apply `fill` if there are no `...` inputs

[DavisVaughan]

library(tidyr)

df <- tibble(a = c(1, 2, 3), c = c(1, NA, 3))
df
#> # A tibble: 3 × 2
#>       a     c
#>   <dbl> <dbl>
#> 1     1     1
#> 2     2    NA
#> 3     3     3

# should apply fill here anyways
complete(df, fill = list(c = 0))
#> # A tibble: 3 × 2
#>       a     c
#>   <dbl> <dbl>
#> 1     1     1
#> 2     2    NA
#> 3     3     3

complete(df, a, fill = list(c = 0))
#> # A tibble: 3 × 2
#>       a     c
#>   <dbl> <dbl>
#> 1     1     1
#> 2     2     0
#> 3     3     3

^{Created on 2021-12-14 by the reprex package (v2.0.1)}