[gtk/bilelmoussaoui/g-i] gtk: add nullable annotation to gtk_css_section_get_file

[Bilal Elmoussaoui <bilelmoussaoui src gnome org>]

commit 90357193c94b0fe57a53bdcf1f15e654f5bae043
Author: Bilal Elmoussaoui <bil elmoussaoui gmail com>
Date:   Sat Jan 1 17:31:38 2022 +0100

    gtk: add nullable annotation to gtk_css_section_get_file
    
    The constructor takes a nullable file param

 gtk/css/gtkcsssection.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gtk/css/gtkcsssection.c b/gtk/css/gtkcsssection.c
index 5851cc201c..727141fdb6 100644
--- a/gtk/css/gtkcsssection.c
+++ b/gtk/css/gtkcsssection.c
@@ -140,7 +140,7 @@ gtk_css_section_get_parent (const GtkCssSection *section)
  * If no such file exists, for example because the CSS was loaded via
  * [method@Gtk.CssProvider.load_from_data], then `NULL` is returned.
  *
- * Returns: (transfer none): the `GFile` from which the `section`
+ * Returns: (transfer none) (nullable): the `GFile` from which the `section`
  *   was parsed
  **/
 GFile *