Think of "module" as something Apache calls, like mod_jk2 or mod_python or mod_perl or XXX... Apache can't very well implement checks to protect those modules from crapping out on r->filename.
it might be a little late in the game for this, but I've always wanted an api encapsulating r->filename.
the main reason was that there are really two things of interest - r->filename and r->finfo - so modules that twiddle r->filename after translation (and map_to_storage, I guess) need to remember to update r->finfo as well if they want later ap_meets_decisions to be made properly.
having an api would certainly make life easier in external modules (like mod_perl), but I suspect would solve so of the NULL issues being raised here, since the checking would be done in a single place.
--Geoff
