[R] "methods" package changes class types?

[Nunoo, Paa K]

Hi,

Loading the "methods" package into R seems to change the class of a
character vector from NULL to "character":

> class("abcd")
NULL
> library("methods")
> class("abcd")
[1] "character"

This can lead to problems. For example the "as.string" function in the
"xtable" package 
assumes that the class of a character vector is NULL. However this changes
when the methods 
package is loaded.

Here is a code snippet of the as.string function in the xtable package:
> library(xtable)
> as.string
function (x, file = "", append = FALSE) 
{
    if (is.null(class(x))) 
        switch(data.class(x), character = return(string(x, file, 
            append)), numeric = return(string(as.character(x), 
            file, append)), stop("Cannot coerse argument to a string"))
    if (class(x) == "string") 
        return(x)
    stop("Cannot coerse argument to a string")
}

Why does the methods package change the class of character vectors?
Is there a way around this behavior?

Thanks,
PK