[bug#38781] [PATCH core-updates] build-system/gnu: Make 'first-subdirectory' optional.

[Danny Milosavljevic]

* guix/build/gnu-build-system.scm (unpack): Make 'first-subdirectory'
optional.
---
 guix/build/gnu-build-system.scm | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/guix/build/gnu-build-system.scm b/guix/build/gnu-build-system.scm
index 4df0bb4904..4ebaa455b0 100644
--- a/guix/build/gnu-build-system.scm
+++ b/guix/build/gnu-build-system.scm
@@ -160,7 +160,7 @@ working directory."
         (if (string-suffix? ".zip" source)
             (invoke "unzip" source)
             (invoke "tar" "xvf" source))
-        (chdir (first-subdirectory "."))))
+        (chdir (or (first-subdirectory ".") "."))))
   #t)
 
 (define %bootstrap-scripts