as.character(list(NA))

| As of R Under development (unstable) (2018-01-19 r74138):
| 
|  > as.character(list(NA))
| [1] "NA"
| 
|  > is.na(as.character(list(NA)))
| [1] FALSE

Are you aware that this is the same in R-release, and might be "on purpose" ?

R> R.Version()$version.string
[1] "R version 3.4.3 (2017-11-30)"
R> as.character(list(NA))
[1] "NA"
R> is.na(as.character(list(NA)))
[1] FALSE
R> 

It is after all you who forces the as.character() and I don't think anybody
claims that to be a lossless operation from logical.  To wit:

R> is.na(list(NA))
[1] TRUE
R> 

Dirk

http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org