I notice in impnotes it says that this doesn't work.
(I also notice it gives an error when I try it.)
This seems to me to be incompatible with the CL spec.
If so it should be changed.
I suppose it's an implementation choice whether this returns
a pathname or nil (if you consider a directory to not be a file),
but I'd suggest an extra keyword argument to control that choice.
Has this been discussed before?
If so I must not have been paying attention.