Function behaves differently when debugged

[Matthias Pfeifer]

Hi everybody,

I have this function

(defun mp-ibuffer-show-file-path ()
  (interactive)
   (let ((buf (ibuffer-current-buffer))
        (lsoutput nil))
    (if (not (null buf))
        (when (file-exists-p (buffer-file-name buf))
          (with-temp-buffer
            (let* ((filename (buffer-file-name buf))
                   (file-directory (file-name-directory filename))
                   (just-filename (file-name-nondirectory filename)))
              (setq lsoutput file-directory))))
      (setq lsoutput "Buffer is not backed by a file"))
    (message lsoutput)))

I bind it to some key in ibuffer-mode. it should print the path to a
buffer's file. When point is on a line of a buffer that is not backed by a
file (eg *Messages*) then i get this output:

wrong type argument: strinp, nil

However when I instantiated my defun for debugging and do the same again I
get

"Buffer is not backed by a file"

The second behavior is actually what i had expected when i was writing the
function. The first behavior is a bit unexpected. Also I do not understand
why my function behaves differently when my defun is debugged and when it
run without debugging.


Thanks for your help.


Matthias