[glibmm] Gio::FileInfo::list_attributes(): Make name_space optional.

[Murray Cumming <murrayc src gnome org>]

commit 6d22f7a4844035f240043513c0ba8b29a8e138a6
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Feb 10 18:43:30 2016 +0100

    Gio::FileInfo::list_attributes(): Make name_space optional.
    
    Because I noticed that this has just been documented as being allowed
    to be null:
    https://git.gnome.org/browse/glib/commit/?id=a4ed89bf75190631087596be22f9eb10dc6e53ef

 gio/src/fileinfo.hg |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gio/src/fileinfo.hg b/gio/src/fileinfo.hg
index 9d31ba4..54841f9 100644
--- a/gio/src/fileinfo.hg
+++ b/gio/src/fileinfo.hg
@@ -99,7 +99,7 @@ public:
   _WRAP_METHOD(bool has_namespace(const std::string& name_space) const, g_file_info_has_namespace)
 
   #m4 _CONVERSION(`char**',`Glib::StringArrayHandle',`Glib::StringArrayHandle($3, Glib::OWNERSHIP_DEEP)')
-  _WRAP_METHOD(Glib::StringArrayHandle list_attributes(const std::string& name_space) const,
+  _WRAP_METHOD(Glib::StringArrayHandle list_attributes(const std::string& name_space{?}) const,
                g_file_info_list_attributes)
 
   _WRAP_METHOD(FileAttributeType get_attribute_type(const std::string& attribute) const,