not operator for `is.na()`

The "not" operator does not work for is.na():

suppressMessages(library("frab"))
(x <- frab(c(x=5,y=1,z=2)))
#> A frab object with entries
#> x y z 
#> 5 1 2
x["y"] <- NA
is.na(x)
#> A disind object with hash eec061606d73bf83eced3b5d7d31b5b14459f96f and 1 (implementation-specific) elements
!is.na(x)
#> Error in !is.na(x): invalid argument type

Now I don't think that "!is.na(x)" should work, but it is not documented clearly.

RobinHankin / frab

not operator for `is.na()` #15