[Rd] Warning: use of NULL environment is deprecated (in R CMD check)

[hadley wickham]

* checking S3 generic/method consistency ... WARNING
Warning: use of NULL environment is deprecated
Warning: use of NULL environment is deprecated
See section 'Generic functions and methods' of the 'Writing R Extensions'
manual.

I don't get any other warnings or errors.  Can anyone suggest what the
problem might be? (R2.3.0, OS X)

Thanks,

Hadley