## The Null Object

## Usage

    NULL
    as.null(x)
    is.null(x)

## Description

`NULL` represents the null object in R. NULL is used mainly to represent the lists with zero length, and 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.

## Examples

    is.null(list())    # TRUE (not so in S)
    is.null(integer(0))# F
    is.null(logical(0))# F
    as.null(list(a=1,b='c'))

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