(wrong-type-argument stringp nil) in latest git head

[lvh]

Since updating to latest git head, I get the following error on startup (well, this is the backtrace I get when I pass --debug-init):

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  file-exists-p(nil)
  (if (file-exists-p python-check) (progn (defvar python-check-command python-check "Command used to check a Python file.")))
  (when (file-exists-p python-check) (defvar python-check-command python-check "Command used to check a Python file."))
  (let* ((elpy-el (or byte-compile-current-file buffer-file-name)) (python-check (when elpy-el (concat (file-name-directory elpy-el) "python-check.sh")))) (when (file-exists-p python-check) (defvar python-check-command python-check "Command used to check a Python file.")))
  eval-buffer(#<buffer  *load*<2>> nil "/Users/lvh/.emacs.d/elpy/elpy.el" nil t)  ; Reading at buffer position 1965

This happens regardless of whether or not I set python-check-command. python-check's value is nil, but that might be related to the error.

[lvh]

Using git-bisect, I was able to find the commit that causes this error on startup:

a353ff678475d0c3c0e67c19ecc94c8fd864e158 is the first bad commit
commit a353ff678475d0c3c0e67c19ecc94c8fd864e158
Author: Jorgen Schaefer <forcer@forcix.cx>
Date:   Sun Feb 3 13:29:17 2013 +0100

    New build environment: Build a .tar for Marmalade/Elpa.

    The new build script `build.sh` will create the appropriate directory
    and tar file, including the elpy-pkg.el from the new file
    elpy-pkg.el.in with all the dependencies. Those have been remove from
    elpy.el.

    python-check.sh is now included in the tarfile, and elpy.el will
    initialize python-check-command with it if it can be found.

    Fixes #13

:000000 100755 0000000000000000000000000000000000000000 a46b22975019c16b7e74ea0c074701af052dcf22 A  build.sh
:000000 100644 0000000000000000000000000000000000000000 1b7e196e43ff3a3474dd74e997b15a1761981b53 A  elpy-pkg.el.in
:100644 100644 affc2992deede845b8fe069efde92eb7eb4df95b 7fdba53af4003c3928788c502a09e94904b619d7 M  elpy.el

Hope that helps :)