roxygen2 fails to generate method documentation

[yxomo]

roxygen2 fails to generate documentation for a simple S4 method with only one parameter. I am giving example code with class A and method B below:

#' A Class
#'
#' Example class.
#'
#' @name A-class
#' @rdname A-class
#' @exportClass A
setClass("A", representation(), prototype = prototype())

setGeneric("B", function(.Object) standardGeneric("B"))

#' B-methods
#'
#' Example method on class A.
#'
#' @return The given object, invisibly.
#'
#' @docType methods
#' @rdname B-methods
#' @aliases B,A-method
#' @export
setMethod("B", "A",
        function(.Object) {
            return(invisible(.Object))
        }
)

[Geoff99]

Hi
I think I have some insight into which line of code generates this issue - but I don't know enough to have a suggested fix yet.
I posted details on the devtools group (since that is the route by which I began using roxygen2) at
https://groups.google.com/forum/#!topic/rdevtools/2TMDbDcPNA8
Importantly I subsequently realised part of my post was not correct and added a correction as a reply to that message.
I think the problem lies within roxygen2::get_rd see the devtools post or an extract below for why.
Hope this is helpful.
Geoff

Summary of where the problem emerges

inherit_from calls get_rd(generic, package)

get_rd <- function (topic, package = NULL) 
{
    help_call <- substitute(help(t, p), list(t = topic, p = package))
    top <- eval(help_call)
    if (length(top) == 0) 
        return(NULL)
    internal_f("utils", ".getHelpFile")(top)
}

get_rd includes a line

top <- eval(help_call)

That is where the problem arises if the .Rd file for the generic does not already exist. An error is raised, and eventually devtools::document() falls over.

If the help file for the generic is found, eval returns something which makes the rest of the code happy.