\Header{NULL}{The Null Object}
\alias{as.null}{NULL}
\methalias{as.null.default}{NULL}
\alias{is.null}{NULL}
\keyword{attribute}{NULL}
\keyword{manip}{NULL}
\keyword{list}{NULL}
\keyword{sysdata}{NULL}
\begin{Description}\relax
\code{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.

\code{as.null} ignores its argument and returns the value \code{NULL}.

\code{is.null} returns \code{TRUE} if its argument
is \code{NULL} and \code{FALSE} otherwise.\end{Description}
\begin{Usage}
\begin{verbatim}
NULL
as.null(x)
is.null(x)
\end{verbatim}
\end{Usage}
\begin{Examples}
\begin{ExampleCode}
is.null(list())    # FALSE (on purpose!)
is.null(integer(0))# F
is.null(logical(0))# F
as.null(list(a=1,b='c'))
\end{ExampleCode}
\end{Examples}

