How to detect an empty quosure in rlang?

f <- function(x) enquo(x)

e <- f()
#<quosure: empty>
#~

None of these work:

> is_empty(e)
[1] FALSE
> is_missing(e)
[1] FALSE
> is_false(e)
[1] FALSE
> is_quosure(e)
[1] TRUE