[libhandy] expander-row: Make the subtitle nullable

[Alexander Mikhaylenko <alexm src gnome org>]

commit 905054cb373c4659583d3b75e42709ad0782e985
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Mon Jul 27 10:18:47 2020 +0200

    expander-row: Make the subtitle nullable
    
    This matches the title, making the widget more consistent.

 src/hdy-expander-row.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/hdy-expander-row.c b/src/hdy-expander-row.c
index a6a7f5e1..55bf6952 100644
--- a/src/hdy-expander-row.c
+++ b/src/hdy-expander-row.c
@@ -440,7 +440,7 @@ hdy_expander_row_new (void)
  *
  * Gets the subtitle for @self.
  *
- * Returns: the subtitle for @self.
+ * Returns: (transfer none) (nullable): the subtitle for @self, or %NULL.
  *
  * Since: 1.0
  */
@@ -459,7 +459,7 @@ hdy_expander_row_get_subtitle (HdyExpanderRow *self)
 /**
  * hdy_expander_row_set_subtitle:
  * @self: a #HdyExpanderRow
- * @subtitle: the subtitle
+ * @subtitle: (nullable): the subtitle
  *
  * Sets the subtitle for @self.
  *