Change to "pbcopy" command in 4.1?

I have an AppleScript that contains the following:

tell document 1 of application "OmniOutliner"
    pbcopy selected rows
end tell

But after upgrading to 4.1, this gives an error:

error “OmniOutliner got an error: Some parameter is missing for pbcopy.” number -1701

The dictionary for “pbcopy” now indicates that it takes a “from tree” parameter, but nowhere is “tree” defined. Is it the document? the application? the top-level row containing the selection?


I would also like more info on this.