\name{union-class}
\docType{class}
\alias{listOrNull-class}
\alias{integerOrNull-class}
\alias{vectorNamesType-class}
\title{Some useful class unions}
\description{ The class "listOrNull" is a union of the classes "list"
  and "NULL". The class "listOrNull" is a union of the classes "list"
  and "NULL". The class "vectorNamesType" is a union of the classes
  "character", "NULL" and "externalVectorWithStorage".
}
\section{Objects from the Class}{These are virtual classes: no objects may be created from them.}
\section{Methods}{
No methods defined with class "listOrNull", "integerOrNull" or
"vectorNamesType" in the signature.
}
\keyword{classes}