[libgit2-glib] Fix documentation for error indicating it can be NULL

[Jesse van den Kieboom <jessevdk src gnome org>]

commit 6aed57555836113a00d973b8e5665de0b3eea604
Author: Jesse van den Kieboom <jesse vandenkieboom epfl ch>
Date:   Tue Jul 17 14:49:02 2012 +0200

    Fix documentation for error indicating it can be NULL

 libgit2-glib/ggit-tree.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libgit2-glib/ggit-tree.c b/libgit2-glib/ggit-tree.c
index 483d8cc..6b11a99 100644
--- a/libgit2-glib/ggit-tree.c
+++ b/libgit2-glib/ggit-tree.c
@@ -185,7 +185,7 @@ walk_callback_wrapper (const char           *root,
  * @callback: (scope call): the callback to call for each entry
  * @mode: the walking order
  * @user_data: (closure): user data for the callback.
- * @error: a #GError.
+ * @error: a #GError for error reporting, or %NULL.
  *
  * Walk all the entries of a tree object recursively (resolving and walking
  * subtrees of the tree as needed). The @error will be set to the error returned