NULL represents the null object in R: it is a reserved
word. NULL is often returned by expressions and functions
whose value is undefined.
as.null ignores its argument and returns the value NULL.
is.null returns TRUE if its argument
is NULL and FALSE otherwise.
Usage
NULL
as.null(x, ...)
is.null(x)
Arguments
x
an object to be tested or coerced.
...
ignored.
Details
NULL can be indexed (see Extract) in just about any
syntactically legal way: whether is makes sense or not, the result is
always NULL. Objects with value NULL can be changed by
replacement operators and will be coerced to the type of the
right-hand side.