image: Add default value for partition initializer.

Previously, the default value would lead to a wrong-type-to-apply crash.

* gnu/system/image.scm (system-disk-image)[image-builder]: When
'partition-initializer' returns #f, fall back to
INITIALIZE-ROOT-PARTITION.
* gnu/tests/base.scm (run-root-unmount-test)[test-image]: Remove
'initializer' field of partition.
* gnu/image.scm (<partition>)[initializer]: Add comment.

1 files changed, 1 insertions, 1 deletions

diff --git a/gnu/image.scm b/gnu/image.scm
index e10a495d3d2..e347089b342 100644
--- a/gnu/image.scm
+++ b/gnu/image.scm
@@ -70,7 +70,7 @@
   (label                partition-label (default #f))
   (uuid                 partition-uuid (default #f))
   (flags                partition-flags (default '()))
-  (initializer          partition-initializer (default #f)))
+  (initializer          partition-initializer (default #f))) ;gexp | #f
 
 
 ;;;