[R] Function failure in tm

[Simon Kiss]

HI all:
I have a customized source reader for the package tm (that Milan Bouchet-Vallat has been instrumental in producing). 
I can get it to produce a corpus of class:
"VCorpus" "Corpus"  "list"   

class(mycorp[1]) returns
"VCorpus" "Corpus"  "list"   

and class(mycorp[[1]] returns 
"PlainTextDocument" "TextDocument"      "character"   

But now that I've got a corpsu, none of the transformation functions work at all. They all return the following error (with the respective function name)
Error in UseMethod("stripWhitespace", x) : 
  no applicable method for 'stripWhitespace' applied to an object of class "NULL"

I haven't seen this error reported anywhere in the R-list archives.  Does anyone have any suggestions?
Yours, Simon Kiss

P.S. The results of sessionInfo() are
R version 2.15.0 (2012-03-30)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)

locale:
[1] en_CA.UTF-8/en_CA.UTF-8/en_CA.UTF-8/C/en_CA.UTF-8/en_CA.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] RWekajars_3.7.7-2     rJava_0.9-3           RWeka_0.4-13          Snowball_0.0-8       
[5] tm.plugin.factiva_1.1 tm_0.5-8.1           

loaded via a namespace (and not attached):
[1] grid_2.15.0  slam_0.1-26  tools_2.15.0 XML_3.9-4